List of U.S. state and territory abbreviations
This table includes abbreviations for three independent countries related to the United States through Compacts of Free Association, and other comparable postal abbreviations, including those now obsolete.
|Name and status of region||ISO||ANSI||USPS||USCG||GPO||AP||Other|
|United States of America||Federal state||US
|District of Columbia||Federal district||US-DC||DC||11||DC||DC||D.C.||D.C.||Dis. Col. |
|Kentucky||State||US-KY||KY||21||KY||KY||Ky.||Ky.||Ken., Kent. [b]|
|New Jersey||State||US-NJ||NJ||34||NJ||NJ||N.J.||N.J.||N. Jersey |
|New Mexico||State||US-NM||NM||35||NM||NM||N. Mex.||N.M.||New M., New Mex.|
|New York||State||US-NY||NY||36||NY||NY||N.Y.||N.Y.||N. York |
|North Carolina||State||US-NC||NC||37||NC||NC||N.C.||N.C.||N. Car.|
|North Dakota||State||US-ND||ND||38||ND||ND||N. Dak.||N.D.|
|Ohio||State||US-OH||OH||39||OH||OH||Ohio||Ohio||O.,  Oh. |
|Pennsylvania||State||US-PA||PA||42||PA||PA||Pa.||Pa.||Penn.,  Penna. |
|Rhode Island||State||US-RI||RI||44||RI||RI||R.I.||R.I.||R.I. & P.P.|
|South Carolina||State||US-SC||SC||45||SC||SC||S.C.||S.C.||S. Car.|
|South Dakota||State||US-SD||SD||46||SD||SD||S. Dak.||S.D.||SoDak|
|West Virginia||State||US-WV||WV||54||WV||WV||W. Va.||W.Va.||W.V., W. Virg.|
|American Samoa||Insular area ( Territory)||AS
|Guam||Insular area (Territory)||GU
|Northern Mariana Islands||Insular area ( Commonwealth)||MP
|Puerto Rico||Insular area ( Commonwealth)||PR
|U.S. Virgin Islands||Insular area (Territory)||VI
|U.S. Minor Outlying Islands||Insular areas||UM
|Baker Island||Island||UM-81||81||XB |
|Howland Island||Island||UM-84||84||XH |
|Jarvis Island||Island||UM-86||86||XQ |
|Johnston Atoll||Atoll||UM-67||67||XU |
|Kingman Reef||Atoll||UM-89||89||XM |
|Midway Islands||Atoll||UM-71||71||QM |
|Navassa Island||Island||UM-76||76||XV |
|Palmyra Atoll [c]||Atoll [c]||UM-95||95||XL |
|Wake Island||Atoll||UM-79||79||QW |
|Marshall Islands||Freely associated state||MH
|Micronesia||Freely associated state||FM
|Palau||Freely associated state||PW
|U.S. Armed Forces – Americas [d]||US military mail code||AA|
|U.S. Armed Forces – Europe [e]||US military mail code||AE|
|U.S. Armed Forces – Pacific [f]||US military mail code||AP|
|Nebraska||Obsolete postal code [g]||NB|
|Northern Mariana Islands||Obsolete postal code [h]||CM|
|Panama Canal Zone||Obsolete postal code||PZ
|Philippine Islands||Obsolete postal code||PH
|Trust Territory of the Pacific Islands||Obsolete postal code||PC
As early as October 1831, the United States Post Office recognized common abbreviations for states and territories. However, they accepted these abbreviations only because of their popularity, preferring that patrons spell names out in full to avoid confusion. 
The traditional abbreviations for U.S. states and territories, widely used in mailing addresses prior to the introduction of two-letter U.S. postal abbreviations, are still commonly used for other purposes (such as legal citation), and are still recognized (though discouraged) by the Postal Service. 
Modern two-letter abbreviated codes for the states and territories originated in October 1963, with the issuance of Publication 59: Abbreviations for Use with ZIP Code, three months after the Post Office introduced ZIP codes in July 1963. The purpose, rather than to standardize state abbreviations per se, was to make room in a line of no more than 23 characters for the city, the state, and the ZIP code. 
The two-letter postal abbreviation system is complicated by the fact that several state names begin with the same letter (e.g., eight state names begin with M and eight begin with N, four "New" and two "North"). To avoid duplications, some abbreviations are not intuitive.
Prior to 1987, when the U.S. Secretary of Commerce approved the two-letter codes for use in government documents,  the United States Government Printing Office (GPO) suggested its own set of abbreviations, with some states left unabbreviated. Today, the GPO supports United States Postal Service standard. 
The American National Standards Institute (ANSI) established alphabetic and numeric codes for each state and outlying areas in ANSI standard INCITS 38:2009. ANSI standard INCITS 38:2009 replaced the Federal Information Processing Standard (FIPS) standards FIPS 5-2, FIPS 6-4, and FIPS 10-4. The ANSI alphabetic state code is the same as the USPS state code except for U.S. Minor Outlying Islands, which have an ANSI code "UM" but no USPS code—and U.S. Military Mail locations, which have USPS codes ("AA", "AE", "AP") but no ANSI code.
The United States Postal Service (USPS) has established a set of uppercase abbreviations to help process mail with optical character recognition and other automated equipment.  There are also official USPS abbreviations for other parts of the address, such as street designators (street, avenue, road, etc.).
These two-letter codes are distinguished from traditional abbreviations such as Calif., Fla., or Tex. The Associated Press Stylebook states that in contexts other than mailing addresses, the traditional state abbreviations should be used.  However, the Chicago Manual of Style now recommends use of the uppercase two-letter abbreviations, with the traditional forms as an option. 
The postal abbreviation is the same as the ISO 3166-2 subdivision code for each of the fifty states.
These codes do not overlap with the 13 Canadian subnational postal abbreviations. The code for Nebraska changed from NB to NE in November 1969 to avoid a conflict with New Brunswick.  Canada likewise chose MB for Manitoba to prevent conflict with either Massachusetts (MA), Michigan (MI), Minnesota (MN), Missouri (MO), or Montana (MT).
The U.S. Coast Guard (USCG) uses a set of two-letter prefixes for vessel numbers;  39 states and the District of Columbia have the same USPS and USCG abbreviations. USCG prefixes have also been established for five outlying territories; all are the same as the USPS abbreviations except the Mariana Islands. The twelve cases where USPS and USCG abbreviations differ are listed below and marked in bold red in the table above, and do include three inland states with a small Coast Guard contingent. These twelve abbreviations were changed to avoid conflicting with the ISO 3166 two-digit country codes.
- Australian abbreviation system
- Canadian abbreviation system
- ISO 3166-2:US
- United States Postal Service address formatting information
- "Ioa." or (more typically) "IOA" found in Iowa post office cancellations from the 1870s.
- Not to be confused with Kent, England
- The Palmyra Atoll is an unorganized incorporated territory of the United States that was previously a part of the Territory of Hawaii.
- The U.S. Armed Forces – Americas include the Caribbean Sea and exclude the United States, Canada, and Greenland.
- The U.S. Armed Forces – Europe include the Atlantic Ocean, the Mediterranean Sea, Canada, Greenland, Africa, and Southwest Asia.
- The U.S. Armed Forces – Pacific include the Indian Ocean, Oceania, and Asia except Southwest Asia.
- Former USPS code "NB" for Nebraska is now obsolete; it was changed to NE in November 1969 to avoid confusion with New Brunswick, Canada.
- Former USPS code "CM" for the Commonwealth of the Northern Mariana Islands is now obsolete; it was changed to MP in 1988 to match ISO 3166-1.
- Consolidated Listing of FAA Certificated Repair Stations. U.S. Dept. of Transportation. December 9, 1970. Retrieved March 12, 2020.
- USPS Postal History: State Abbreviations Accessed November 7, 2011.
- Arthur, Andy. "Penna. the Abbreviation". AndyArthur.org. Retrieved February 15, 2021.
- Fisher, Richard S. (1857). A new and complete statistical gazetteer of the United States of America. J. H. Colton and Company. Retrieved March 12, 2020.
- "search on WN". Digitum.washingtonhistory.org. Retrieved February 26, 2018.
- "Commonwealth of the Northern Mariana Islands". www.doi.gov. Retrieved January 7, 2018.
- "Geopolitical Entities, Names, and Codes Standard". NSG Standards Registry. Retrieved February 6, 2017.
- "Philippine diplomats will now use PH or PHL instead of RP". GMA News. October 28, 2010. Retrieved March 17, 2013.
- "USPS Postal News, "It's Okay to Say 'I Don't Know,' So Long As You Find Out!" January 9, 2009". About.usps.com. January 9, 2009. Retrieved February 26, 2018.
- Hawes, Kristi G. (May 28, 1987). "Information Technology Laboratory". NIST. Archived from the original on July 5, 2009. Retrieved April 21, 2009.
- U.S. Government Printing Office Style Manual, 30th Edition  Accessed April 21, 2009.
- United States Postal Service (June 2020). "Appendix B. Two–Letter State and Possession Abbreviations. Postal Addressing Standards". Postal Explorer. Retrieved January 21, 2020.
- Robbins, Sonia J. (January 4, 2004). "State Abbreviations". New York University. Archived from the original on April 24, 2009.
- Harper, Russell David, ed. (2017) . "10.27 Abbreviations for US states and territories". The Chicago manual of style (17th ed.). The University of Chicago Press.
In bibliographies, tabular matter, lists, and mailing addresses, they are usually abbreviated. In all such contexts, Chicago prefers the two-letter postal codes to the conventional abbreviations.
- 33 CFR 173, App. A