March 20, 2026
US State Abbreviations: The Complete Guide (And Why They Aren't Always Obvious)
You know CA is California and NY is New York. But why is Louisiana LA instead of LO? Why is Michigan MI but Minnesota MN? And what was the Post Office thinking when it assigned ME to Maine and not Maryland? The two-letter state abbreviation system looks simple until you try to explain the logic. Here is the full story — every code, every conflict, every oddity.
Before 1963: The Wild West of Abbreviations
Before the US Post Office standardized abbreviations in 1963, states had no official short codes. People wrote whatever felt natural. California might appear as "Cal." or "Calif." or "Ca." Pennsylvania was variously "Penn.", "Penna.", or "Pa." Massachusetts was "Mass." — always. This chaos worked well enough when mail was sorted by humans who could read context clues. But in the early 1960s, the Post Office began planning for automated sorting machines that needed a consistent, fixed-length code.
In October 1963, the Post Office Department published Publication 59, establishing two-letter abbreviations for all 50 states, the District of Columbia, and US territories. The system was designed for machines, not humans. That is why some codes feel intuitive and others feel baffling. The goal was uniqueness, not memorability.
The Rules (Such as They Are)
The Post Office followed loose principles, not rigid rules. Here is the pattern that emerges when you study all 50 codes:
Rule 1: First two letters of a one-word name. This works cleanly for states with unique starting pairs: Alabama (AL), Alaska (AK), Arizona (AZ), Colorado (CO), Connecticut (CT), Delaware (DE), Florida (FL), Georgia (GA), Hawaii (HI), Idaho (ID), Illinois (IL), Indiana (IN), Iowa (IA), Kansas (KS), Kentucky (KY), Louisiana (LA), Montana (MT), Nebraska (NE), Nevada (NV), Ohio (OH), Oklahoma (OK), Oregon (OR), Texas (TX), Utah (UT), Vermont (VT), Virginia (VA), Wisconsin (WI), Wyoming (WY).
Rule 2: First letter + a distinguishing consonant. When the first two letters conflict, the Post Office grabbed a consonant from deeper in the name. Michigan (MI) got the first two letters. Minnesota (MN) grabbed the N. Mississippi (MS) grabbed the S. Missouri (MO) grabbed the O. Maine (ME) grabbed the E. Maryland (MD) grabbed the D. Massachusetts (MA) grabbed the A. That is eight M-states resolved without duplicates — shown in the diagram above.
Rule 3: Two-word states use initials. New Hampshire (NH), New Jersey (NJ), New Mexico (NM), New York (NY), North Carolina (NC), North Dakota (ND), Rhode Island (RI), South Carolina (SC), South Dakota (SD), West Virginia (WV). Simple, clean, no conflicts.
The Ones That Break the Rules
Some abbreviations seem to defy logic until you understand the conflict they were dodging:
Pennsylvania — PA. Why not PE? Because PE was too close to the common abbreviation for Prince Edward Island (a Canadian province that confused mail sorters in border regions). PA echoes the traditional "Pa." that Pennsylvanians had always used.
Tennessee — TN. TE was available, but TN mirrors the spoken rhythm of the name better — "Ten-nes-see" — and avoids any visual confusion with TX (Texas). The N comes from the second syllable.
Washington — WA. Not WS, not WT, but WA. This one actually follows Rule 1 (first two letters) perfectly. The confusion is entirely on the human side — people mix up Washington the state with Washington, D.C. (DC). The abbreviation itself is straightforward; the name collision is the problem.
Louisiana — LA. This is the one everyone asks about. Why not LO? Because LA was already the dominant informal abbreviation ("La." had been used since colonial times), and LO was considered too easy to misread as a number (10) on handwritten envelopes. The L-O combination looked ambiguous to sorting machines with 1960s-era optical character recognition.
The Most Commonly Confused Pairs
Even after 60+ years, certain pairs trip people up consistently. Here are the codes that geography teachers, postal workers, and trivia players report mixing up most often:
MI (Michigan) vs. MN (Minnesota) vs. MS (Mississippi) vs. MO (Missouri): The M-cluster is the single hardest group. All four are Midwestern or Southern states beginning with M-I or M-I-S. The key: Michigan takes the I, Minnesota takes the N, Mississippi takes the S, Missouri takes the O. Mnemonic: "I Now See Ohio" — the second letters spell I-N-S-O.
AL (Alabama) vs. AK (Alaska) vs. AZ (Arizona) vs. AR (Arkansas): Four A-states, four different second letters. Alabama gets L (natural), Alaska gets K (from its last syllable — "alas-KA"), Arizona gets Z (the most distinctive consonant in its name), Arkansas gets R.
ME (Maine) vs. MD (Maryland) vs. MA (Massachusetts): The Northeast M-states. Maine and Maryland are especially tricky because both are small, East Coast states that people sometimes conflate. ME is Maine (think "ME, I live in Maine"). MD is Maryland (think "Maryland, D.C. neighbor").
The Complete List: All 50 State Abbreviations
For reference, here is every state and its code, grouped by the first letter. States that follow the "first two letters" rule are unmarked. States that required a non-obvious choice are marked with an asterisk (*).
A: AL, AK*, AZ*, AR* C: CA, CO, CT D: DE F: FL G: GA H: HI I: ID, IL, IN, IA* K: KS*, KY* L: LA* M: ME*, MD*, MA*, MI, MN*, MS*, MO*, MT N: NE, NV*, NH, NJ, NM, NY, NC, ND O: OH, OK, OR P: PA* R: RI S: SC, SD T: TN*, TX* U: UT V: VT, VA W: WA, WV, WI, WY
Test Your Knowledge
Knowing abbreviations is useful for trivia, mail, and data analysis. But knowing where each state actually sits on the map is a different challenge. The Just States quiz on GeoProwl asks you to click on each state when given its name — ten seconds per state, all 50 in a row. It is a fast, unforgiving test of geographic knowledge. Or try the daily GeoProwl challenge, where you guess states from real government data clues — no abbreviation hints, just Census and USDA statistics.
For a visual twist, our silhouette quiz strips away all labels and asks you to identify states by their outline alone. And if you want the full data profile for any state, check the Fast Facts directory — demographics, agriculture, climate, health, and national parks for all 50.
The next time someone asks why Louisiana is LA and not LO, you will have the answer: blame the optical character recognition technology of 1963.