View source for ZIP Code

{{Short description|Numeric postal code used in the US and its territories}}
{{other uses|Zip code (disambiguation)}}
{{Use American English|date=July 2022}}
{{Use mdy dates|date=July 2022}}
[[File:USA-Stamp-1973-ZIPCode.jpg|thumb|A 1974 postage stamp encouraging people to use the ZIP Code on letters and parcels]]

The '''ZIP Code''' system (an acronym for '''Zone Improvement Plan'''<ref>{{cite web |title=Flashing Across the Country: Mr. Zip and the ZIP Code Promotional Campaign |url=https://postalmuseum.si.edu/flashing-across-the-country |publisher=Smithsonian National Postal Museum |access-date=30 May 2023 |first=Abby |last=Curtin |archive-date=May 30, 2023 |archive-url=https://web.archive.org/web/20230530154715/https://postalmuseum.si.edu/flashing-across-the-country |url-status=live }}</ref>) is the system of [[postal code|postal codes]] used by the [[United States Postal Service]] (USPS). The term ''ZIP'' was chosen to suggest that the [[mail]] travels more efficiently and quickly<ref>{{Cite web|url=https://www.uspsoig.gov/sites/default/files/document-library-files/2015/rarc-wp-13-006_0.pdf|title=The Untold Story of the ZIP Code|date=April 1, 2013|publisher=U.S. Postal Service Office of Inspector General|access-date=March 11, 2020|quote=When Day unveiled the nationwide 5-digit ZIP Code at a postmasters' convention in October of 1962, he simultaneously introduced the world to 'Mr. ZIP'—the cartoon character whose body language symbolizes speedy delivery.|archive-date=December 29, 2016|archive-url=https://web.archive.org/web/20161229123814/https://www.uspsoig.gov/sites/default/files/document-library-files/2015/rarc-wp-13-006_0.pdf|url-status=dead}}</ref> ([[wikt:zip#Verb|zipping along]]) when senders include the code in the [[Address (geography)|postal address]]. ''ZIP+4'' is a registered trademark of the United States Postal Service, which also registered ''ZIP Code'' as a [[service mark]] until 1997,<ref>{{cite web |title=Latest Status Info |url=http://tarr.uspto.gov/servlet/tarr?regser=serial&entry=73001312 |url-status=live |archive-url=https://web.archive.org/web/20120630044408/http://tarr.uspto.gov/servlet/tarr?regser=serial |archive-date=June 30, 2012 |access-date=22 December 2019 |publisher=[[United States Patent and Trademark Office]]}}</ref> and which claims "ZIP Code" as a trademark though it is not registered.<ref>{{cite web |title=USPS Trademarks |url=https://about.usps.com/strategic-planning/cs09/CSPO_09_001.htm |access-date=26 May 2025}}</ref>

Introduced on July 1, 1963, the basic format was five digits, the first designating a region of the country and subsequent digits localizing the destination further.<ref name="mlcdintr">{{cite news |url=https://news.google.com/newspapers?id=ubNWAAAAIBAJ&sjid=0-gDAAAAIBAJ&pg=7238%2C4744197 |work=Spokesman-Review |location=Spokane, Washington |agency=Associated Press |title=Post office readies new area mailing code |date=June 30, 1963 |page=9}}</ref><ref name="lblsccs">{{cite news |url=https://news.google.com/newspapers?id=-LZWAAAAIBAJ&sjid=7OgDAAAAIBAJ&pg=3401%2C1173278 |work=Spokesman-Review |location=Spokane, Washington |agency=Associated Press |title=ZIP Code is labeled a success |date=October 4, 1963 |page=6}}</ref><ref>{{Cite web |last=Terrell |first=Ellen |title=This Month in Business History: ZIP Code Introduced |url=https://guides.loc.gov/this-month-in-business-history/july/zip-code-introduced |access-date=2022-07-31 |work=Library of Congress Research Guides |language=en |date=June 28, 2013 |archive-date=October 29, 2021 |archive-url=https://web.archive.org/web/20211029214050/https://guides.loc.gov/this-month-in-business-history/july/zip-code-introduced |url-status=live }}</ref> In 1983, an extended code was introduced named ''ZIP+4''; it included the five digits of the ZIP Code, followed by a hyphen and four digits that designated a location even more specific than the original five. 

Private carriers and the USPS use ZIP Codes to route deliveries. In addition, ZIP Codes have become a basis for breaking down demographic, marketing, and sales data for analytical purposes.

== History ==

=== Early postal zones ===
[[File:UseZipCode.JPG|thumb|A 1963 U.S. Post Office sign featuring [[Mr. ZIP]]]]
[[File:Stamps USA, Markenheft IMG 1699.JPG|thumb|A [[Label (philately)|label]] inside a [[Postage stamp booklet|stamp booklet]] promoting the ZIP Code]]
[[File:Swinging Six Zip Code 1967.ogv|thumb|thumbtime=14:38|right|320px|A Swingin' Six video used by the post office to promote the ZIP Code]]
The early history and context of postal codes began with [[Postal code#History|postal district/zone numbers]]. The [[United States Post Office Department]] (USPOD) implemented postal zones for 124 large cities in May 1943.<ref>{{Cite web |title=A Zoning System in Development |url=https://postalmuseum.si.edu/zipcodecampaign/p2.html |archive-url=https://web.archive.org/web/20120104222751/http://www.postalmuseum.si.edu/zipcodecampaign/p2.html |archive-date=2012-01-04 |url-status=dead |publisher=Smithsonian National Postal Museum |access-date=2019-12-22}}</ref> Postmaster General [[Frank C. Walker]] explained that many experienced postal clerks were going into the army, and the zone system would enable inexperienced clerks to sort mail without having to learn the delivery area of each city carrier.<ref>{{cite news |title=Home Folks to Have P.O. Numbers Like Army Boys |url=https://www.newspapers.com/image/182725652/?terms=postal%20zone&match=1 |access-date=31 January 2023 |publisher=Minneapolis Morning Tribune |date=May 6, 1943 |archive-date=February 1, 2023 |archive-url=https://web.archive.org/web/20230201032632/https://www.newspapers.com/image/182725652/?terms=postal%20zone&match=1 |url-status=live }}</ref>

For example:

<blockquote>
<poem>
Mr. John Smith
3256 Epiphenomenal Avenue
Minneapolis ''16'', Minnesota
</poem>
</blockquote>

The "16" is the number of the postal zone in a specific city.<ref name=":0">{{Cite web|url=https://www.theatlantic.com/technology/archive/2013/04/the-bounty-zip-codes-brought-america/275233/|title=The Bounty ZIP Codes Brought America|last=Chokshi|first=Niraj|date=April 23, 2013|website=The Atlantic|language=en-US|access-date=2020-03-12|quote=...Postmaster General Edward Day in the early 1960s suggested combining Moon's three-digit code with the existing two-digit system.|archive-date=October 26, 2020|archive-url=https://web.archive.org/web/20201026095632/https://www.theatlantic.com/technology/archive/2013/04/the-bounty-zip-codes-brought-america/275233/|url-status=live}}</ref>

=== Establishment ===
By the early 1960s, a more organized system was needed. Non-mandatory five-digit ZIP Codes were introduced nationwide on July 1, 1963.<ref name=mlcdintr/><ref name=lblsccs/> The USPOD issued its ''Publication 59: Abbreviations for Use with ZIP Code'' on October 1, 1963, with the list of [[List of U.S. state abbreviations|two-letter state abbreviations]] which are generally written with both letters capitalized.<ref name=USPS>[https://about.usps.com/who-we-are/postal-history/state-abbreviations.pdf "State Abbreviations", USPS.com] {{Webarchive|url=https://web.archive.org/web/20170116005935/http://about.usps.com/who-we-are/postal-history/state-abbreviations.pdf |date=2017-01-16 }}.</ref> An earlier list, publicized in June 1963, had proposed capitalized abbreviations ranging from two to five letters.<ref name=USPS/> According to ''Publication 59'', the two-letter standard was "based on a maximum 23-position line, because this has
been found to be the most universally acceptable line capacity basis for major addressing systems",<ref name=USPS/> which would be exceeded by a long city name combined with a multi-letter state abbreviation, such as "Sacramento, Calif." along with the ZIP Code. The abbreviations have remained unchanged, except for [[Nebraska]], which was changed from NB to NE in 1969 at the request of the [[Canada Post|Canada Post Corporation]], to avoid confusion with [[New Brunswick]].<ref name=USPS/>

[[Robert Moon (postal inspector)|Robert Moon]] is considered the father of the ZIP Code; he submitted his proposal in 1944 while working as a [[United States Postal Inspection Service|postal inspector]].<ref>Bullamore, Tim (2001). Robert Moon Obituary. Retrieved from https://www.independent.co.uk/news/obituaries/robert-moon-729034.html {{dead link|date=December 2019}}.</ref><ref>{{cite news | url = https://www.nytimes.com/2001/04/14/us/robert-moon-an-inventor-of-the-zip-code-dies-at-83.html | title = Robert Moon, an Inventor of the ZIP Code, Dies at 83 | first = Douglas | last = Martin | date = 2001-04-14 | newspaper = [[New York Times]] | access-date = 2017-09-23 | archive-date = February 17, 2020 | archive-url = https://web.archive.org/web/20200217102920/https://www.nytimes.com/2001/04/14/us/robert-moon-an-inventor-of-the-zip-code-dies-at-83.html | url-status = live }}</ref> 

The phrase "zone improvement plan" is credited to [[D. Jamison Cain]], a Postal Service executive.<ref name="cain">{{Cite news |url=https://www.washingtonpost.com/local/virginia-resident-pushed-the-envelope-when-zip-code-was-born-in-1963/2018/09/29/38376e7a-c28c-11e8-97a5-ab1e46bb3bc7_story.html |title=Virginia resident pushed the envelope when Zip code was born in 1963 |date=2018-09-29 |last=Kelly |first=John |newspaper=[[The Washington Post]] |access-date=2022-08-13 |archive-date=October 10, 2018 |archive-url=https://web.archive.org/web/20181010205600/https://www.washingtonpost.com/local/virginia-resident-pushed-the-envelope-when-zip-code-was-born-in-1963/2018/09/29/38376e7a-c28c-11e8-97a5-ab1e46bb3bc7_story.html |url-status=live }}</ref> The post office credits Moon with only the first three digits of the ZIP Code, which describe the [[sectional center facility]] (SCF) or "sec center". An SCF is a central mail processing facility with those three digits. The fourth and fifth digits, which give a more precise locale within the SCF, were proposed by Henry Bentley Hahn Sr.<ref>{{Cite web|url=http://archiveblog.jfklibrary.org/2015/05/papers-of-h-bentley-hahn-the-man-who-invented-the-zip-code/|title=Papers of H. Bentley Hahn: The Man Who Invented the 5-Digit ZIP Code |website=Archivally Speaking |first1=Lauren |last1=Wallace |date= May 15, 2015 |publisher=John F. Kennedy Presidential Library Archives |language=en-US|access-date=2018-04-30|archive-url=https://web.archive.org/web/20180501095121/http://archiveblog.jfklibrary.org/2015/05/papers-of-h-bentley-hahn-the-man-who-invented-the-zip-code/|archive-date=2018-05-01|url-status=dead}}</ref>

The SCF sorts mail to all post offices with those first three digits in their ZIP Codes. The mail is sorted according to the final two digits of the ZIP Code and sent to the corresponding post offices in the early morning. Sectional centers do not deliver mail and are not open to the public, although the building may include a post office that is open to the public, and most of their employees work the [[shift work|night shift]]. Items of mail picked up at post offices are sent to their SCFs in the afternoon, where the mail is sorted overnight. In the case of large cities, the last two digits as assigned generally coincided with the older postal zone number.<ref name=":0" />

For example:

<blockquote>
<poem>
Mr. John Smith
3256 Epiphenomenal Avenue
Minneapolis, MN{{nbsp}}{{nbsp}}554''16''
</poem>
</blockquote>

In 1967, these became mandatory for second- and third-class bulk mailers, and the system was soon adopted generally. The United States Post Office used a [[cartoon]] character, which it called [[Mr. ZIP]], to promote the use of the ZIP Code.<ref name="mrzip">{{Cite web|title=Mr. ZIP- The nation's original 'digital' icon|url=https://about.usps.com/who-we-are/postal-history/mr-zip.pdf|url-status=dead|archive-url=https://web.archive.org/web/20090508223728/https://www.usps.com/postalhistory/_pdf/MrZIP.pdf|archive-date=2009-05-08}}</ref> The name "Mr. ZIP" was coined by D. Jamison Cain.<ref name="cain"/> Mr. ZIP was often depicted with a legend such as "USE ZIP CODE" in the [[selvage]] of panes of [[postage stamp]]s or on the covers of booklet panes of stamps.<ref name="mrzip"/> Mr. ZIP was featured prominently alongside musical group "The Swingin' Six" in a variety show that the post office used to explain the importance of using ZIP Codes.<ref>{{Cite web|date=2013-07-01|title=The US Postal Service's zip code system turns 50|url=https://www.scpr.org/programs/take-two/2013/07/01/32505/the-us-postal-services-zip-code-system-turns-50/|access-date=2020-06-16|website=Southern California Public Radio|archive-date=June 16, 2020|archive-url=https://web.archive.org/web/20200616062613/https://www.scpr.org/programs/take-two/2013/07/01/32505/the-us-postal-services-zip-code-system-turns-50/|url-status=live}}</ref>

===ZIP+4===
In 1983, the U.S. Postal Service introduced an expanded ZIP Code system that it named ''ZIP+4'', often known as "plus-four codes", "add-on codes", or "add-ons". A ZIP+4 Code uses the basic five-digit code plus four additional digits to identify a geographic segment within the five-digit delivery area, such as a city block, a group of apartments, an individual high-volume receiver of mail, a post office box, or any other unit that could use an extra identifier to aid in efficient mail sorting and delivery. However, the new format was not adopted universally by the public.<ref>{{cite web|url=http://www.randomhistory.com/zip-code-history.html|title=Organizing America: A History of the ZIP Code|date=25 July 2014|website=RandomHistory.com|publisher=Random History|url-status=dead|archive-url=https://web.archive.org/web/20140812203838/http://www.randomhistory.com/zip-code-history.html|archive-date=12 August 2014|access-date=19 June 2017}}</ref>

Commercial customers generally apply a ZIP+4 or a delivery point code (i.e., ZIP+6) to mail as part of address normalization. They may need to do so to receive discounted postage rates.<ref>{{Cite journal |date=11 July 2013 |title=New Standards to Enhance Package Visibility |url=https://www.govinfo.gov/content/pkg/FR-2013-07-11/pdf/2013-16524.pdf |journal=[[Federal Register]] |volume=78 |issue=133 |pages=41721–41731}}</ref> The public does not need to write the ZIP+4 code, as mail is read by a [[Multiline Optical Character Reader|multiline optical character reader]] (MLOCR) that almost instantly determines the correct ZIP+4 Code from the address—along with the even more specific [[delivery point]]—and sprays an [[Intelligent Mail barcode]] (IMb) on the face of the mail piece that corresponds to 11 digits—nine for the ZIP+4 Code and two for the delivery point.

For [[post office box]]es, the general but not invariable rule is that each box has its own ZIP+4 Code. The add-on code is often one of the following: the last four digits of the box number (e.g. PO Box 107050, Albany, NY 12201-7050), zero plus the last three digits of the box number (e.g., PO Box 17727, Eagle River, AK 99577-0727), or, if the box number consists of fewer than four digits, enough zeros are attached to the front of the box number to produce a four-digit number (e.g., PO Box 77, Juneau, AK 99750-0077). However, there is no uniform rule, so the ZIP+4 Code must be looked up individually for each box (e.g. using the USPS's official ZIP Code Lookup tool, and being sure to enter just city and state, not the 5-digit ZIP).<ref>{{cite web |url=https://tools.usps.com/go/ZipLookupAction_input |title=ZIP Code™ Lookup {{!}} USPS |website=tools.usps.com |access-date=2020-01-23 |archive-date=December 22, 2016 |archive-url=https://web.archive.org/web/20161222044440/https://tools.usps.com/go/ZipLookupAction_input |url-status=live }}</ref>

===Postal barcode===
{{main|Intelligent Mail barcode}}
The ZIP Code is often translated into an Intelligent Mail barcode printed on the mailpiece to make it easier for automated machines to sort. A barcode can be printed by the sender (some word-processing programs such as [[WordPerfect]]<ref>{{cite web |url=http://kb.iu.edu/data/aapk.html |title=Archived: How can I print routing barcodes on envelopes? – Knowledge Base |publisher=The Trustees of Indiana University |access-date=July 10, 2009 |archive-date=March 10, 2012 |archive-url=https://web.archive.org/web/20120310180946/http://kb.iu.edu/data/aapk.html |url-status=live }}</ref> include the feature), but this is not recommended, as the address-to-ZIP lookup tables can be significantly out of date.

Customers who send bulk mail can get a [[Discounts and allowances|discount]] on postage if they have printed the barcode and have presorted the mail. This requires more than just a simple [[typeface|font]]; [[mailing list]]s must be standardized with up-to-date [[Coding Accuracy Support System]] (CASS)-certified software that adds and verifies a full, correct ZIP+4 Code and an additional two [[Numerical digit|digit]]s representing the exact [[delivery point]].{{citation needed|date=April 2010}} Furthermore, mail must be sorted in a specific manner to an 11-digit code with at least 150 mailpieces for each qualifying ZIP Code. It must be accompanied by documentation confirming this. These steps are usually done with PAVE-certified software that prints the barcoded address labels and the barcoded sack or tray tags.{{citation needed|date = November 2018}}

The assignment of delivery point digits (the 10th and 11th digits) ensures that every mailable point in the country has an 11-digit number. The delivery-point digits are calculated based on the primary or secondary number of the address. The USPS publishes the rules for calculating the delivery point in a document called the CASS Technical Guide.<ref>{{cite web |url=http://www.ribbs.usps.gov/files/CASS/TECHNICAL_GUIDES/CASSTECH.PDF#page=40 |format=PDF |title=CASS Technical Guide |publisher=United States Postal Service |page=40 |access-date=July 10, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090419090333/http://ribbs.usps.gov/files/CASS/TECHNICAL_GUIDES/CASSTECH.PDF#page=40 |archive-date=April 19, 2009 }}</ref>

==Structure and allocation==
ZIP Codes designate [[delivery point]]s within the United States (and its territories). 

===Types===

There are four types of ZIP Codes:

* Unique: assigned to a single high-volume address
* Post office box-only: used only for PO boxes at a given facility, not for any other type of delivery
* Military: used to route mail for the U.S. military
* Standard: all other ZIP Codes.

Unique ZIP Codes are used for governmental agencies, universities, businesses, prisons, or buildings receiving sufficiently high volumes of mail to justify the assignment to them of exclusive ZIP Codes. Government examples include 20505 for the [[Central Intelligence Agency]] in Washington, D.C., and 81009 for the [[Federal Citizen Information Center]] of the [[U.S. General Services Administration]] (GSA)<ref>{{cite web |url=http://www.pueblo.gsa.gov/aboutus.htm |title=FCIC&nbsp;– About Us |publisher=Federal Citizen Information Center of the U.S. General Services Administration |access-date=July 10, 2009 |quote=For years, consumers have written to Pueblo, Colorado 81009 for timely, practical information they trust. |url-status=dead |archive-url=https://web.archive.org/web/20090714061028/http://www.pueblo.gsa.gov/aboutus.htm |archive-date=July 14, 2009 }}</ref> in [[Pueblo, Colorado]]. An example of a university-specific ZIP Code is 21252, which serves [[Towson University]]. An example of a unique ZIP Code assigned to a prison is 81290 for the [[Federal Correctional Complex, Florence|Federal Correctional Complex]] near [[Florence, Colorado]].  An example of a private address with a unique ZIP Code is that assigned to the headquarters of [[Walmart]] (72716). They may also be assigned to a single individual, such as [[Smokey Bear]] "20252", or a program, such as the Postal Service's [[Operation Santa Claus]] program, under which children are invited to write to Santa Claus at "North Pole 88888".<ref>{{Cite web |last=Miller |first=Susan |title='Don't forget about me': USPS' Operation Santa looking for donors to make magic this year |url=https://www.usatoday.com/story/news/nation/2022/11/14/usps-operation-santa-adopt-letters/8307694001/ |access-date=2022-12-02 |website=USA TODAY |language=en-US |archive-date=November 24, 2022 |archive-url=https://web.archive.org/web/20221124204758/https://www.usatoday.com/story/news/nation/2022/11/14/usps-operation-santa-adopt-letters/8307694001/ |url-status=live }}</ref>

An example of a PO box-only ZIP Code is 22313, used for boxes at the main post office in [[Alexandria, Virginia]], including those used by the [[United States Patent and Trademark Office]]. In the area surrounding that post office, home and business mail delivery addresses use ZIP Code 22314, a standard ZIP Code.

===Geographic hierarchy===

====Primary state prefixes====
[[File:ZIP Code zones.svg|thumb|ZIP Code zones in the United States]]

ZIP Codes are numbered with the first digit representing a certain group of U.S. states, the second and third digits together representing a [[region]] in that group (or perhaps a large city), and the fourth and fifth digits representing a group of delivery addresses within that region. The main town in a region (if applicable) often gets the first ZIP Codes for that region; afterward, the numerical order often follows the alphabetical order.{{citation needed|date=April 2010}} Because ZIP Codes are intended for efficient postal delivery, there are unusual cases where a ZIP Code crosses state boundaries, such as a military facility spanning multiple states or remote areas of one state most easily serviced from a bordering state. For example, ZIP Code 42223 serves [[Fort Campbell]], which spans [[Christian County, Kentucky]], and [[Montgomery County, Tennessee]], and ZIP Code 97635 includes portions of [[Lake County, Oregon]], and [[Modoc County, California]].

The first three digits generally designate a [[sectional center facility]], the area's mail sorting and distribution center. A sectional center facility may have more than one three-digit code assigned to it. For example, the Northern Virginia sectional center facility in [[Merrifield, Virginia|Merrifield]] is assigned codes 220, 221, 222, and 223. In some cases, a sectional center facility may serve an area in an adjacent state, usually due to the lack of a proper location for a center in that region. For example, 739 in Oklahoma is assigned to [[Amarillo, Texas]]; 297 in [[South Carolina]] is assigned to [[Charlotte, North Carolina]]; 865 in Arizona is assigned to [[Albuquerque, New Mexico]]; and 961 in [[California]] to [[Reno, Nevada]].

Many of the lowest ZIP Codes, which begin with&nbsp;'0', are in the [[New England]] region. In the '0' region are New Jersey (non-contiguous with the remainder of the '0' area), [[Puerto Rico]], the [[U.S. Virgin Islands]], and [[APO/FPO]] military addresses for personnel stationed in Europe, Africa, Southwest Asia, and onboard vessels based in the waters adjoining those lands. The lowest ZIP Code is in [[Holtsville, New York]] (00501, a ZIP Code exclusively for the U.S. [[Internal Revenue Service]] center there).<ref>{{cite web |url=https://facts.usps.com/map/#fact147 |title=USPS Postal Facts |publisher=facts.usps.com |date=2018-02-15 |access-date=2018-05-31 |archive-url=https://web.archive.org/web/20180819070643/https://facts.usps.com/map/#fact147 |archive-date=2018-08-19 |url-status=dead }}</ref> Other low ZIP Codes are 00601 for [[Adjuntas, Puerto Rico]]; 01001 for [[Agawam, Massachusetts]], and the ZIP Codes 01002 and 01003 for [[Amherst, Massachusetts]]; 01002 is used for mail in town, while the [[University of Massachusetts Amherst]] primarily uses 01003. Until 2001, there were six ZIP Codes lower than 00501 that were numbered from 00210 to 00215 (located in [[Portsmouth, New Hampshire]]) and were used by the [[Diversity Immigrant Visa]] program to receive applications from non-U.S. citizens.{{citation needed|date=April 2010}}

The numbers increase southward along the [[East Coast of the United States|East Coast]], such as 02115 ([[Boston]]), 10001 ([[New York City]]), 19103 ([[Philadelphia]]), 21201 ([[Baltimore]]), 20008 ([[Washington, D.C.]]), 30303 ([[Atlanta]]), and 33130 (Miami) (these are only examples, as each of these cities contains several ZIP Codes in the same range). From there, the numbers increase heading westward and northward east of the [[Mississippi River]], southward west of the Mississippi River, and northward on the [[West Coast of the United States|West Coast]]. For example, 40202 is in [[Louisville, Kentucky|Louisville]], 50309 in [[Des Moines, Iowa|Des Moines]], 60601 in [[Chicago]], 63101 in [[St. Louis]], 77036 in [[Houston]], 80202 in [[Denver]], 94111 in [[San Francisco]], 98101 in [[Seattle]], and 99950 in [[Ketchikan, Alaska]] (the highest ZIP Code).

The first digit of the ZIP Code is allocated as follows:

* 0 = [[Connecticut]] (CT), [[Massachusetts]] (MA), [[Maine]] (ME), [[New Hampshire]] (NH), [[New Jersey]] (NJ), [[New York (state)|New York]] (NY, [[Fishers Island, New York|Fishers Island only]]), [[Puerto Rico]] (PR), [[Rhode Island]] (RI), [[Vermont]] (VT), [[Virgin Islands]] (VI), Army Post Office Europe, Central Asia, and the Middle East (APO AE); Fleet Post Office Europe and the Middle East (FPO AE)
* 1 = [[Delaware]] (DE), [[New York (state)|New York]] (NY), [[Pennsylvania]] (PA)
* 2 = [[District of Columbia]] (DC), [[Maryland]] (MD), [[North Carolina]] (NC), [[South Carolina]] (SC), [[Virginia]] (VA), [[West Virginia]] (WV)
* 3 = [[Alabama]] (AL), [[Florida]] (FL), [[Georgia (U.S. state)|Georgia]] (GA), [[Mississippi]] (MS), [[Tennessee]] (TN), Army Post Office Americas (APO AA), Fleet Post Office Americas (FPO AA)
* 4 = [[Indiana]] (IN), [[Kentucky]] (KY), [[Michigan]] (MI), [[Ohio]] (OH)
* 5 = [[Iowa]] (IA), [[Minnesota]] (MN), [[Montana]] (MT), [[North Dakota]] (ND), [[South Dakota]] (SD), [[Wisconsin]] (WI)
* 6 = [[Illinois]] (IL), [[Kansas]] (KS), [[Missouri]] (MO), [[Nebraska]] (NE)
* 7 = [[Arkansas]] (AR), [[Louisiana]] (LA), [[Oklahoma]] (OK), [[Texas]] (TX)
* 8 = [[Arizona]] (AZ), [[Colorado]] (CO), [[Idaho]] (ID), [[New Mexico]] (NM), [[Nevada]] (NV), [[Utah]] (UT), [[Wyoming]] (WY)
* 9 = [[Alaska]] (AK), [[American Samoa]] (AS), [[California]] (CA), [[Guam]] (GU), [[Hawaii]] (HI), [[Marshall Islands]] (MH), [[Federated States of Micronesia]] (FM), [[Northern Mariana Islands]] (MP), [[Oregon]] (OR), [[Palau]] (PW), [[Washington (state)|Washington]] (WA), Army Post Office Pacific (APO AP), Fleet Post Office Pacific (FPO AP)

====Secondary regional prefixes (123xx) and local ZIP Codes (12345)====
{{See also|List of ZIP Code prefixes}}
[[File:10005 zip code.jpg|thumb|Early advertisement for ZIP Code 10005]]

The second and third digits represent the [[sectional center facility]] (SCF) (e.g., 477xx = [[Vanderburgh County, Indiana]]). The fourth and fifth digits represent the area of the city (if in a [[metropolitan area]]), or a village/town (outside metro areas), e.g., 47722 (4=Indiana, 77=Vanderburgh County, 22=[[University of Evansville]] area). When a sectional center facility's area crosses state lines, it is assigned separate three-digit prefixes for the states it serves.

In some urban areas, like 462 for [[Marion County, Indiana]], the three-digit prefix will often exist in one county, while, in rural and most suburban areas, the prefix will exist in multiple counties; for example, the neighboring 476 prefix is found in part or entirely in six counties: Gibson, Pike, Posey, Spencer, Vanderburgh, and Warrick. In some cases, an urban county may have more than one prefix. This is the case with Allen (467, 468), Lake (464, 463), St. Joseph (465, 466), and Vanderburgh (476, 477) counties. Cities like [[Chicago]], [[Houston]], [[Los Angeles]], and [[New York City]] have multiple prefixes within their city limits. In some cases, these may be served from the same SCF, such as in [[San Diego County, California]], where the three-digit prefixes 919 and 920 are used for suburban and rural communities, and 921 for the city of San Diego itself, although all three are processed through the same SCF.{{citation needed|date=December 2007}}

Despite the geographic derivation of most ZIP Codes, the codes do not represent geographic regions; generally, they correspond to address groups or delivery routes. Consequently, ZIP Code "areas" can overlap, be subsets of each other, or be artificial constructs with no geographic area (such as 095 for mail to the Navy, which is not geographically fixed). Similarly, in areas without regular postal routes ([[Rural delivery service|rural route]] areas) or no mail delivery (undeveloped areas), ZIP Codes are not assigned or are based on sparse delivery routes, and hence the boundary between ZIP Code areas is undefined. For example, some residents in or near [[Haubstadt, Indiana]], which has the ZIP Code 47639, have mailing addresses with 47648, the ZIP Code for neighboring [[Fort Branch, Indiana]], while others living in or near Fort Branch have addresses with 47639. Many rural counties have similar logistical inconsistencies caused by the sparse delivery routes, often called Rural Routes or other similar designations.

==== International mail ====
There are generally no ZIP Codes for deliveries to other countries, except for the independent countries of the [[Federated States of Micronesia]], the [[Republic of the Marshall Islands]], and the [[Republic of Palau]], each of which is integrated into the U.S. postal system under a [[Compact of Free Association]].<ref>{{Cite web |date=2019-07-24 |title=Freely Associated States |url=https://www.doi.gov/ocl/freely-associated-states |url-status=live |archive-url=https://web.archive.org/web/20220520215245/https://www.doi.gov/ocl/freely-associated-states |archive-date=May 20, 2022 |access-date=2022-04-20 |website=www.doi.gov |language=en}}</ref> Another exception is ZIP Codes used for overseas stations of U.S. armed forces.<ref>{{cite web |title=Military Addresses |url=https://pe.usps.com/text/pub28/28c2_010.htm |url-status=live |archive-url=https://web.archive.org/web/20181215222409/https://pe.usps.com/text/pub28/28c2_010.htm |archive-date=December 15, 2018 |access-date=December 15, 2018 |publisher=[[United States Postal Service]]}}</ref>

Mail to [[List of diplomatic missions of the United States|U.S. diplomatic missions]] overseas is addressed as if it were addressed to a street address in [[Washington, D.C.]] The four-digit [[diplomatic pouch]] number is used as a building number, while the city in which the embassy or consulate is located is combined with the word "Place" to form a fictional street name. Each mission uses a ZIP+4 Code consisting of '''20521''' and the diplomatic pouch number.{{Citation needed|date=April 2022}}

For example, the [[Embassy of the United States, New Delhi|U.S. Embassy in India]] has this address in India's postal system:<ref>{{cite web |title=U.S. Embassy and Consulates in India |url=https://in.usembassy.gov/ |url-status=live |archive-url=https://web.archive.org/web/20220128174246/https://in.usembassy.gov/ |archive-date=January 28, 2022 |access-date=September 23, 2022}}</ref>

<blockquote>
<poem>
Embassy of the United States of America
Shantipath, Chanakyapuri,
New Delhi,
National Capital Territory of Delhi, [[Postal Index Number|110021]]
</poem>
</blockquote>

as well as this U.S. address:<ref>{{cite web |title=Mail Management |url=https://2009-2017.state.gov/m/a/c8028.htm |url-status=live |archive-url=https://web.archive.org/web/20190630191152/https://2009-2017.state.gov/m/a/c8028.htm |archive-date=June 30, 2019 |access-date=April 1, 2015 |publisher=Diplomatic Pouch and Mail Division of the U.S. Department of State}}</ref>

<blockquote>
<poem>
Embassy of the United States of America
9000 New Delhi Place
Washington, DC{{nbsp}}{{nbsp}}20521-9000
</poem>
</blockquote>

Individuals posted at diplomatic missions overseas are now assigned a Diplomatic Post Office address and a unique box number. The ZIP Code identifies the diplomatic mission destination and differs from the diplomatic pouch number in the example above. While delivered through the pouch system, mail to such addresses is not considered "Diplomatic Pouch" material and must adhere to the mailing regulations of the host country. An example address is:<ref>{{cite web |title=Military & Diplomatic Mail {{!}} USPS |url=https://www.usps.com/ship/apo-fpo-dpo.htm |url-status=dead |archive-url=https://web.archive.org/web/20190819001108/https://www.usps.com/ship/apo-fpo-dpo.htm |archive-date=19 August 2019 |access-date=8 August 2019 |website=www.usps.com}}</ref>

<blockquote>
<poem>
JOHN ADAMS
UNIT 8400 BOX 0000
DPO AE{{nbsp}}{{nbsp}}09498-0048
</poem>
</blockquote>

=== Division and reallocation ===
Like [[Telephone numbering plan|area code]]s, ZIP Codes are sometimes divided and changed, especially when a [[rural]] area becomes [[suburb]]an. Typically, the new codes become effective once announced, and a grace period (e.g., six months) is provided in which the new and old codes are used concurrently so that postal patrons in the affected area can notify correspondents, order new stationery, etc.<ref>{{cite news |first=Sam |last=Roberts |url=https://www.nytimes.com/2007/03/21/nyregion/21zip.html |title=An Elite ZIP Code Becomes Harder to Crack |work=[[The New York Times]] |date=March 21, 2007 |page=C15 |access-date=July 10, 2009 |archive-date=January 26, 2021 |archive-url=https://web.archive.org/web/20210126211652/http://www.nytimes.com/2007/03/21/nyregion/21zip.html |url-status=live }}</ref>

Opening a new sectional center facility is sometimes necessary in rapidly growing communities, which must then be allocated three-digit ZIP-code prefixes. Such allocation can be done in various ways. For example, when a new sectional center facility was opened at [[Washington Dulles International Airport|Dulles Airport]] in Virginia, the prefix 201 was allocated to that facility; therefore, for all post offices to be served by that sectional center facility the ZIP Code changed from an old code beginning with 220 or 221 to a new code or codes starting with 201. However, no new prefix was assigned when a new sectional center facility was opened to serve [[Montgomery County, Maryland]]. Instead, ZIP Codes in the 207 and 208 ranges, which had previously been assigned alphabetically, were reshuffled so that 207xx ZIP Codes in the county were changed to 208xx codes, while 208xx codes outside that county were changed to 207xx codes. Because [[Silver Spring, Maryland|Silver Spring]] (whose postal area includes [[Wheaton, Maryland|Wheaton]]) has its own prefix, 209, there was no need to apply the reshuffling to Silver Spring; instead, all mail going to 209xx ZIP Codes was simply rerouted to the new sectional center facility.

On the other hand, [[depopulation]] may cause a post office to close and its associated ZIP Code to be deallocated. For example, [[Centralia, Pennsylvania]]'s ZIP Code, 17927, was retired in 2002,<ref>{{cite news |first=Rob |last=Wheary |url=http://www.centraliapa.com/news.htm |title=Centralia loses its ZIP |access-date=2010-05-02 |archive-date=2012-03-24 |archive-url=https://web.archive.org/web/20120324201418/http://www.centraliapa.com/news.htm |url-status=dead }}</ref> and ZIP Codes for [[Onoville, New York|Onoville]] (14764), [[Elko, New York|Quaker Bridge]] (14771) and [[Red House, New York|Red House]] (14773) in New York were prevented from going into use in 1964 in preparation for the [[Kinzua Dam]]'s completion.<ref name=postofficesclose>{{cite news|title=Post Offices to Close|newspaper=The Bradford Era|date=April 22, 1964}}</ref><ref>{{cite news|title=Final Check-Out|newspaper=Salamanca Republican-Press|date=July 1, 1964}}</ref>

== Relationship with local government boundaries ==
Each ZIP Code has one or more "postal city" names assigned to it. Since a ZIP Code is a collection of delivery points served by a specific physical post office, ZIP Codes often do not coincide with the boundaries of local government units. For example, suburban and [[Unincorporated area|unincorporated areas]] may share a postal city name with a neighboring municipality, even if no part of its ZIP Code is actually within that city.<ref>{{Cite web |last=Stevens |first=Nye |date=2006-06-23 |title=Changing Postal ZIP Code Boundaries |url=https://sgp.fas.org/crs/misc/RL33488.pdf |access-date=2024-09-09 |publisher=Congressional Research Service |pages=2}}</ref>

== Other uses ==
=== Delivery services ===
Delivery services other than the USPS, such as [[FedEx]], [[United Parcel Service]], and [[DHL]], require a ZIP Code for optimal internal routing of a package.<ref>{{Cite web|url=https://faq.usps.com/s/article/ZIP-Code-The-Basics|title=USPS.com FAQs|website=faq.usps.com|access-date=2019-02-21|archive-url=https://web.archive.org/web/20190222151852/https://faq.usps.com/s/article/ZIP-Code-The-Basics|archive-date=2019-02-22|url-status=dead}}</ref>

=== Statistics ===
{{As of|2025|10|14|df=US}}, there are 41,557 ZIP Codes in the United States.<ref>{{Cite web|url=https://postalpro.usps.com/areadist_ZIP5|title=Area District 5-digit ZIP Codes|publisher=United States Postal Service|accessdate=October 19, 2025}}</ref> Due to convenience, ZIP Codes are used not only for tracking of mail, but also commonly for gathering geographical statistics in the United States by some researchers.<ref name="Grubesic1">{{cite journal |last1=Grubesic |first1=Tony H |last2=Matisziw |first2=Timothy C |title=On the use of ZIP codes and ZIP code tabulation areas (ZCTAs) for the spatial analysis of epidemiological data |journal=International Journal of Health Geographics |date=2006 |volume=58 |issue=5 |page=58 |doi=10.1186/1476-072X-5-58|doi-access=free |pmid=17166283 |pmc=1762013 }}</ref><ref name="Chen1">{{cite journal |last1=Xiang |first1=Chen |last2=Ye |first2=Xinyue |last3=Widener |first3=Michael J. |last4=Delmelle |first4=Eric |last5=Kwan |first5=Mei-Po |last6=Shannon |first6=Jerry |last7=Racine |first7=Elizabeth F. |last8=Adams |first8=Aaron |last9=Liang |first9=Lu |last10=Jia |first10=Peng |title=A systematic review of the modifiable areal unit problem (MAUP) in community food environmental research |journal=Urban Informatics |date=27 December 2022 |volume=22 |issue=1 |article-number=22 |doi=10.1007/s44212-022-00021-1|doi-access=free |bibcode=2022UrbIn...1...22C }}</ref> ZIP Codes are not created for statistical analysis, and thus their use for statistical analysis is heavily criticized for numerous reasons and advised against as a cartographic practice.<ref name="Chen1"/><ref name="Adams1">{{cite journal |last1=Adams |first1=Aaron |last2=Chen |first2=Xiang |last3=Li |first3=Weidong |last4=Zhang |first4=Chuanrong |title=Normalizing the pandemic: exploring the cartographic issues in state government COVID-19 dashboards |journal=Journal of Maps |date=27 Jul 2023 |volume=19 |issue=3 |pages=1–9 |doi=10.1080/17445647.2023.2235385|doi-access=free |bibcode=2023JMaps..19Q...1A }}</ref> As ZIP Codes are not polygons, but collections of mail routes and points, they are unsuitable for publication or distribution of most data.<ref name="Census Bureau1">{{cite web |title=ZIP Code Tabulation Areas (ZCTAs) |url=https://www.census.gov/programs-surveys/geography/guidance/geo-areas/zctas.html |website=U.S. Census Bureau |access-date=26 August 2023 |archive-date=August 26, 2023 |archive-url=https://web.archive.org/web/20230826203531/https://www.census.gov/programs-surveys/geography/guidance/geo-areas/zctas.html |url-status=live }}</ref> Polygons for ZIP Codes are not released by the USPS and instead interpolated by 3rd party vendors.<ref name="Grubesic1" /> These interpolations introduce topological errors and are not standard between vendors.<ref name="Grubesic1" /> The USPS often discontinues, splits, or otherwise modifies ZIP Codes, making continuous space-time analysis challenging, leading to issues with both the [[modifiable areal unit problem]] (MAUP) and [[modifiable temporal unit problem]] (MTUP).<ref name="Grubesic1" /><ref name="Adams1"/> As the ZIP Codes are postal routing numbers, individuals and organizations without concrete spatial locations may be given a number, making it impossible to associate demographic data with them.<ref name="Grubesic1" /> Demographic data is inconsistent between ZIP Codes, and no effort is made to ensure they are proper enumeration units for analysis.<ref name="Grubesic1" /> As ZIP Codes are not made with the same considerations as other enumeration units, and is not possible without committing the [[ecological fallacy]].<ref name="Grubesic1" /><ref name="Chen1"/> This again becomes an issue with the MAUP. They have been found not to have significant correlations with health indicators, which can lead to poor conclusions.<ref name="Chen1"/> Despite these issues, ZIP Codes remain popular among researchers in fields such as public health due to their convenience, public familiarity with them, ability to anonymize subject addresses through aggregation, and possible ignorance of more appropriate enumeration units on the part of researchers.<ref name="Grubesic1" /><ref name="Adams1" />

In an attempt to satisfy demand "by data users for statistical data by ZIP Code area", the [[United States Census Bureau|U.S. Census Bureau]] calculates approximate boundaries of ZIP Code areas, which it calls [[ZIP Code Tabulation Area]]s (ZCTAs).<ref name="Census Bureau1" /><ref name="Grubesic1" /> Statistical census data is then provided for these approximate areas. The geographic data provided for these areas includes the [[latitude]] and [[longitude]] of the center-point of the ZCTAs. ZIP Codes are inherently discrete or ''point-based'' data, as they are assigned only at the point of delivery, not for the spaces between the delivery points. The United States Census Bureau then interpolates this discrete data set to create polygons by attempting to match ZIP Code extents with Census blocks.<ref name="Grubesic1" /> The resulting aereal units represent the approximate extent of the ZIP Code, which are combined to use for mapping and data presentation. The process of creating ZCTAs and their use for statistical analysis is heavily criticized in the literature. First, the creation of ZCTAs from Census blocks encounters issues when a Census block straddles multiple ZIP Codes.<ref name="Grubesic1" /> Addressing this is another instance of the MAUP, and the solution of dividing aggregate units between ZIP Codes causes some individuals to fall into ZCTAs that do not match their ZIP Code.<ref name="Grubesic1" /> The creation of these units is therefore committing the [[ecological fallacy]] by attempting to disaggregate aggregate data. As ZIP Codes are not continuous, not everyone in the United States has one; there are ZIP Codes for non-populated or geographic areas, resulting in there not being one ZCTA for every ZIP Code.<ref name="Grubesic1" /> ZCTAs are not updated as frequently as the USPS updates ZIP Codes, resulting in further temporal analysis issues when ZIP Codes change during a study period.<ref name="Grubesic1" /> Datasets providing a similar approximate geographic extent to ZCTA are commercially available. Despite these issues, ZCTAs are still very popular with researchers in fields like epidemiology, and among government agencies, with some states employing them to publish and distribute public health data during the COVID-19 pandemic.<ref name="Adams1" />

=== Marketing ===
The data is often used in [[Advertising mail|direct mail marketing]] campaigns in ZIP-code marketing. [[Point of sale|Point-of-sale]] cashiers sometimes ask consumers for their home ZIP Codes. Besides providing purchasing-pattern data useful in determining the location of new business establishments, retailers can use directories to correlate this ZIP Code with the name on a credit card to obtain a consumer's full address and [[telephone number]]. ZIP-Coded data are also used in analyzing geographic risk factors, an insurance and banking industry practice pejoratively known as [[redlining]]. This can cause problems, ''e.g.'', expensive insurance, for people living near a town with a high crime rate and sharing its ZIP Code, while they live in a relatively crime-free town.

California outlawed this practice in 2011.<ref>{{Cite news | title=California high court: Retailers can not request cardholders' ZIP Code | url=http://www.cnn.com/2011/US/02/10/california.credit.zip.code/index.html | last=Botelho | first=Greg | publisher=CNN | date=February 10, 2011 | access-date=February 11, 2011 | archive-date=November 10, 2012 | archive-url=https://web.archive.org/web/20121110023619/http://www.cnn.com/2011/US/02/10/california.credit.zip.code/index.html | url-status=live }}</ref>

=== Legislative districts ===
ZIP Codes may not currently be used to identify existing legislative districts. Although the website of the [[United States House of Representatives]] has a "Find Your Representative" feature that looks up congressional districts based on ZIP Codes alone, it often returns multiple districts corresponding to a single ZIP Code.<ref>{{Cite web|url = http://www.house.gov/|title = The United States House of Representatives · House.gov|access-date = January 26, 2010|archive-date = September 24, 2010|archive-url = https://web.archive.org/web/20100924145826/http://baic.house.gov/|url-status = live}}</ref><ref>{{Cite web|url = http://www.house.gov/representatives/find/|title = Find Your Representative · House.gov|access-date = July 8, 2014|archive-date = July 8, 2014|archive-url = https://web.archive.org/web/20140708212246/http://www.house.gov/representatives/find/|url-status = live}}</ref> This is because different parts of one ZIP Code can be in different districts.<ref>{{Cite web|url = http://sunlightfoundation.com/blog/2012/01/19/dont-use-zipcodes/|title = Sunlight Foundation|date = Jan 19, 2012|access-date = Aug 6, 2014|archive-url = https://web.archive.org/web/20140813005420/http://sunlightfoundation.com/blog/2012/01/19/dont-use-zipcodes/|archive-date = August 13, 2014|url-status = dead}}</ref> One proposal to eliminate the possibility of extreme partisan [[gerrymandering]] calls on using ZIP Codes as the basic units for redistricting.<ref>{{Cite web |last1=Steelman |first1=Tyler |last2=Curiel |first2=John |title=Here's one way to end partisan gerrymandering: Don't break up Zip codes |url=https://www.washingtonpost.com/news/monkey-cage/wp/2018/10/22/heres-one-way-to-end-partisan-gerrymandering-dont-break-up-zip-codes/ |website=Monkey Cage blog |publisher=Washington Post |access-date=4 November 2018 |date=October 22, 2018 |archive-date=November 5, 2018 |archive-url=https://web.archive.org/web/20181105012125/https://www.washingtonpost.com/news/monkey-cage/wp/2018/10/22/heres-one-way-to-end-partisan-gerrymandering-dont-break-up-zip-codes/ |url-status=live }}</ref>

=== Internet ===
A 1978 proposal for a nationwide system of community networks suggested using ZIP Codes for [[routing]].<ref name="wilber197802">{{Cite news | url=https://archive.org/stream/byte-magazine-1978-02/1978_02_BYTE_03-02_Hardware_Projects#page/n15/mode/2up | title=CIE Net: A Design for a Network of Community Information Exchanges | work=BYTE | date=February 1978 | access-date=17 October 2013 | author=Wilber, Mike | page=12}}</ref>

ZIP Code data is an integral part of dealer / [[Online locator service|store locator]] software on many [[website]]s, especially [[Bricks and clicks|brick-and-click]] websites. This software processes a user-input ZIP Code and returns a list of store or business locations, usually in the order of increasing distance from the center of the input ZIP Code. As the ZIP Code system is confined to the U.S. Postal network, websites that require ZIP Codes cannot register customers outside the United States. Many sites will purchase postal code data of other countries or make allowances in cases where the ZIP Code is not recognized.{{citation needed|date=March 2022}}

ZIP Codes are regularly used on the Internet to provide a location where an exact address is not necessary (or desirable) but the user's municipality or general location is needed. Examples (in addition to the store locator example listed above) include weather forecasts, television listings, local news, and [[Online dating service|online dating]] (most general-purpose sites, by default, search within a specified [[radius]] of a given ZIP Code, based on other users' entered ZIP Codes).

=== Credit card security ===
{{Main|Address Verification System}}

ZIP Codes are used in credit card authorization, specifically [[Address Verification System]] (AVS). When a merchant collects the entire address, the ZIP Code is an important part of AVS. In some cases, the ZIP Code is the only thing used for AVS, specifically where collecting a signature or other information is infeasible, such as [[pay at the pump]] or [[vending machine]]s.{{citation needed|date=March 2022}}

== See also ==
{{Portal|Philately|United States}}

* {{Annotated link |J. W. Westcott II|''J. W. Westcott II''}}
* {{Annotated link |Postal codes in Canada}}
* {{Annotated link |ZIP codes in the Philippines}}

== References ==
{{refs}}

== External links ==
{{commonscat|ZIP Codes}}
{{wiktionary|zip code}}

* [https://purl.fdlp.gov/GPO/gpo47009 The Untold Story of the ZIP Code] (PDF) – [[United States Postal Service]]
* [https://www.youtube.com/watch?v=l4WGNjSYKNU ZIP Code promo film (1971)] – U.S. National Archives

{{ZIP Code}}
{{USPS}}
{{Americas topic|Postal codes in}}
{{Authority control}}

[[Category:ZIP code| ]]
[[Category:1963 establishments in the United States]]
[[Category:1963 introductions]]
[[Category:Philatelic terminology]]