State Abbreviations

Until 1963 the Post Office Department preferred that state and territorial names be written out in full to avoid confusion, but accepted the popular public practice of abbreviation.

 The Department published lists of preferred state abbreviations in the 1831 Table of Post Offices in the United States and in the United States Postal Guide, first published in 1874. Most of the preferred abbreviations in 1874 remained the same for almost 90 years.

 On July 1, 1963, the Post Office Department implemented the five-digit ZIP (Zone Improvement Program) Code, which was placed after the state name in the last line of an address. To provide room for the new code in the address line, the Department published an initial list of state abbreviations in the June 27, 1963, issue of the Postal Bulletin. Many of these initial abbreviations consisted of four letters.

Four months later, in October 1963, the Department published the now-familiar list of two-letter state abbreviations in Publication 59, Abbreviations for Use with ZIP Code.

The evolution of state abbreviations can be seen in the table below:

Source: Historian, United States Postal Service, December 2011.