U.S. postal abbreviations

Several sets of codes and abbreviations are used to represent the political divisions of the United States for postal addresses, data processing, general abbreviations, and other purposes.

This table includes abbreviations for three independent nations related to the United States through Compacts of Free Association, and other comparable postal abbreviations, including those now obsolete.

As early as October 1831, the United States Post Office recognized common abbreviations for states and territories. However, they only accepted these abbreviations 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.

Since 1963, only one state abbreviation has changed. Originally Nebraska was "NB"; but, in November 1969, the Post Office changed it to "NE" to avoid confusion with New Brunswick in Canada.

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.

...
Wikipedia