Why your mail address dictates the two-letter code for your home state
In short: The two-letter codes we use for states today were not designed for clarity, but for space. Introduced in 1963 to accommodate ZIP codes on a single line of text, these abbreviations transformed how we process mail, yet they remain distinct from the traditional abbreviations still preferred by legal scholars.
Before the modern era of automated mail sorting, the United States Postal Service relied on traditional abbreviations like Calif. or Tex. These were recognized as early as 1831, though officials originally preferred that patrons write out full state names to prevent errors. The shift toward the current two-letter system began in July 1963 with the introduction of ZIP codes. By October of that year, the Post Office issued Publication 59, which established these codes to ensure that city, state, and ZIP code information could fit within a 23-character limit on a single line of mail.
The system is built for machine efficiency, specifically to aid optical character recognition equipment. While these codes are now the standard for the United States Postal Service and match the ISO 3166-2 subdivision codes for all fifty states, they are not universal. Legal citation manuals, such as The Bluebook, continue to favor traditional abbreviations. Even the Chicago Manual of Style, which now permits the two-letter format, still lists the older, longer abbreviations as a viable alternative for non-mailing contexts.
Maintaining these codes requires constant coordination to avoid international confusion. For instance, Nebraska was originally assigned the code NB, but this was updated to NE in November 1969 to prevent conflict with the Canadian province of New Brunswick. Similarly, Canada adopted MB for Manitoba to avoid clashing with several U.S. states, including Massachusetts and Missouri. Further complexity arises from the U.S. Coast Guard, which uses its own prefixes for vessel numbers; in twelve instances, these differ from postal codes to avoid overlap with ISO country codes.
Beyond the postal system, these abbreviations are integrated into broader data standards. The American National Standards Institute maintains codes for states and outlying areas under standard INCITS 38:2009, which replaced older Federal Information Processing Standards. While these ANSI codes largely mirror the postal system, they exclude U.S. Military Mail locations, which possess postal codes like AA or AP but lack a corresponding ANSI designation.
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Sources
- Summary by Intellect · source: List of U.S. state and territory abbreviations
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