Why US State Abbreviations Are 2 Letters: The 1963 ZIP Code Story
Every American address ends the same way: a city, two capital letters, and five numbers. Los Angeles, CA 90001. Austin, TX 78701. But those two letters were not always there — and they were not chosen because somebody liked the way they looked. They exist because of a machine that could only fit 23 characters on one line, and a deadline in the summer of 1963. This is the story of how the ZIP code gave America its state abbreviations, why Mississippi is MS and not MI, and why one state — Nebraska — had to change its code six years later.
Play the US States Abbreviations Quiz
July 1, 1963: The Day the ZIP Code Arrived
On July 1, 1963, the Post Office Department introduced the five-digit ZIP Code — ZIP stands for Zone Improvement Plan. The idea was simple: give every postal region a number so machines could sort mail faster than people could. A letter addressed to Chicago, Illinois would now end with a five-digit code that told the sorting machine exactly where it belonged, and the whole country would get its mail faster. The system worked. What nobody planned for was the problem the numbers created on the line above them: the bottom line of an address — city, state, ZIP code — had to fit the addressing equipment, and most of that equipment could only handle 23 characters, including spaces. “Chicago, Illinois 60601” was already too long before the ZIP code even started. Something had to shrink, and the state name was the obvious target.
Why 23 Characters Changed Everything
The 23-character limit sounds like a small technical detail, but it decided the shape of every American address for the next sixty years. A city name plus a full state name plus five digits plus the spaces and the comma between them had to fit in 23 characters, and for long names it simply did not. “Philadelphia, Pennsylvania 19101” is 32 characters. “Salt Lake City, Utah 84101” is 27. Even a short city with a long state broke the limit. The Post Office had two choices: make the machines bigger, or make the state names shorter. Making the machines bigger would have cost a fortune and taken years. Making the names shorter cost nothing — so in June 1963 the Department issued an initial list of abbreviations. Many of them still had three or four letters, like ALA for Alabama and NEB for Nebraska, and they were still too long to fit reliably. Three months later, in October 1963, the Department settled the question for good: Publication 59, “Abbreviations for Use with ZIP Code”, gave every state exactly two uppercase letters, with no periods and no spaces between them. CA. NY. TX. The two-letter code was born not as a language reform but as a fitting problem — two letters was the longest abbreviation that would always fit.
Why MS Is Not MI: The Eight M-States
The two-letter system had one awkward problem: eight states start with the letter M, and eight start with N. When eight names share a first letter, the second letter has to do all the work, and the obvious second letters run out fast. Michigan took MI — the first two letters of its name. That left Mississippi, Missouri, Minnesota, Maine, Maryland, Massachusetts and Montana to find other letters. Mississippi became MS, taking the S from the double S in the middle of its name. Missouri became MO, taking the O from its second syllable. Minnesota became MN, taking the N. Maine became ME, Maryland MD, Massachusetts MA, Montana MT. None of these is the “obvious” abbreviation, and that is exactly why they are the hardest codes in the quiz: the codes were assigned by elimination, not by spelling. The same thing happened with the N-states. Nebraska is NE, Nevada NV, New Hampshire NH, New Jersey NJ, New Mexico NM, New York NY, North Carolina NC, North Dakota ND — and the pairs NE/NV and NC/ND are the traps that catch even fast players. The codes are not random, but they are not intuitive either. They are a 1963 compromise, frozen in place.
The One Code That Changed: Nebraska
Since October 1963, only one state abbreviation has ever changed. Nebraska started as NB — the natural choice, the first two letters of its name. But NB was also the code for New Brunswick, the Canadian province just across the border, and mail kept going to the wrong country. In November 1969, at the request of the Canadian postal administration, the Post Office changed Nebraska to NE. It was a small change with a big lesson: the codes belong to a whole continent’s mail system, not just to one country. Everything else has stayed exactly as Publication 59 set it. The codes were later adopted as the ISO 3166-2 subdivision codes for the United States, and in 1987 the Secretary of Commerce approved them for use in government documents — which is why the same two letters now appear on everything from driving licences to tax forms.
The Old Abbreviations Before 1963
Before 1963, Americans abbreviated states the long way: Ala. for Alabama, Nebr. for Nebraska, N. Y. for New York, with periods and mixed lengths. The Post Office had recognised common abbreviations as early as October 1831, but it preferred people to spell names out in full, because every abbreviation was a chance to misread an address. Those old forms still survive in some places — lawyers still cite them, and old records are full of them — but the post office stopped recommending them decades ago. The two-letter codes replaced them because machines needed them, and then they outlived the machines: today the codes are how Americans write addresses, fill in forms, label maps, and argue about geography online. A system built for a 23-character machine line became the way a country spells itself.
| State | Code | Why this code |
|---|---|---|
| Maine | ME | First two letters |
| Maryland | MD | M + final D |
| Massachusetts | MA | First two letters |
| Michigan | MI | First two letters — took MI first |
| Minnesota | MN | M + N from the middle |
| Mississippi | MS | M + S from the double S |
| Missouri | MO | M + O from the second syllable |
| Montana | MT | First two letters |
How to Learn the Codes the 1963 Way
The fastest way to learn the fifty codes is to learn them the way the post office assigned them: in collision groups. Drill the eight M-states together until the group feels like one fact, then drill the eight N-states the same way. Then take the quiz: twenty questions, code to state and state to code, with the trap pairs sitting in your options on purpose. Every wrong answer shows you the right code, and every replay draws a fresh twenty from the same fifty. The codes have not changed since 1963 — Nebraska aside — so what you learn today is still right tomorrow.
When were the two-letter state abbreviations introduced?
In October 1963, in Publication 59, “Abbreviations for Use with ZIP Code” — three months after the five-digit ZIP Code arrived on July 1, 1963.
Why are state abbreviations only two letters?
Because the addressing equipment of 1963 could fit only 23 characters on the bottom line of an address — city, state and ZIP code together. Two letters was the longest abbreviation that would always fit.
Why is Mississippi MS and not MI?
Because Michigan took MI first. Mississippi took the S from its double S, Missouri took the O from its second syllable, and Minnesota took the N.
Has any state abbreviation ever changed?
Only one: Nebraska was NB until November 1969, when it changed to NE to avoid confusion with New Brunswick in Canada.
What did people use before 1963?
Longer forms with periods, like Ala. for Alabama, Nebr. for Nebraska and N. Y. for New York. Those old forms still appear in legal writing and old records.
Two letters, born from a machine that could only count to 23 — and still going strong sixty years later. Now test yourself on all fifty: the codes have not changed since 1963, so the only thing left to change is your score. And if you want to practise the other half of the skill — finding the states on the map, not just naming their codes — the free us states quiz map game is the best place to do it.