Why the code is PA
The USPS published its two-letter list in October 1963, months after ZIP codes went live. The city, the state and the new five-digit number all had to sit on one address line, and the older forms were too long for that line.
Pennsylvania already had a shorthand: Pa., the form used in printed datelines. USPS kept the same two letters and dropped the period. Structurally, PA is the first letter of the name plus its last one, since Pennsylvania ends in an A. The obvious alternative, PE, was never in play.
Pennsylvania is also the only state whose name begins with P, so no other state ever competed for the code. The only near neighbours are outside the 50: USPS assigns PR to Puerto Rico and PW to Palau. That is why the trouble with PA has nothing to do with another state and everything to do with one very famous city.
Codes people confuse with PA
| Code | State | Why the mix-up happens |
|---|---|---|
| PR | Puerto Rico | The only other P entry most people ever see in a state dropdown. A fast scroll past PA lands on it. |
| NJ | New Jersey | Philadelphia's metro crosses the Delaware River. Camden and Cherry Hill feel like Philadelphia but are NJ addresses. |
| DE | Delaware | Wilmington shares Philadelphia's commuter belt and TV market, so billing forms in the region collect both codes. |
| MD | Maryland | The Mason-Dixon Line is the PA and MD border. Towns a few miles apart end up filed under the wrong state. |
Pennsylvania touches six states, OH, WV, MD, DE, NJ and NY, plus Lake Erie in its far northwest corner. Six land borders means six chances for a form to be filled in with the neighbour's code.
The bigger error is not a rival code at all. People type PA expecting it to stand for Philadelphia, because the city appears in more headlines than the state does. Philadelphia has its own shorthand and none of it is PA: the airport is PHL, sports tables use PHI, and the state code stays PA whether the address is in Philadelphia, Erie or Scranton.
Quick facts about Pennsylvania
Capital: Harrisburg
Largest city: Philadelphia
Region: Northeast, Mid-Atlantic
Statehood: 1787, the second state to ratify the Constitution
Population band: over 10 million
Nickname: the Keystone State
Pennsylvania is one of the 33 states where the capital is not the largest city. Harrisburg runs the government, Philadelphia carries the population, and Pittsburgh anchors the western half. Its legal name is the Commonwealth of Pennsylvania, one of four states that call themselves a commonwealth rather than a state. The postal code ignores the distinction, and so does every address form you will ever fill in.
Where you will see PA
- Mail. The code sits between the city and the ZIP: Harrisburg, PA followed by five digits. Pennsylvania ZIPs run across the 150 to 196 prefixes, with Pittsburgh at 152 and Philadelphia at 191.
- License plates. The plate spells Pennsylvania out in full. The two-letter form shows up on the registration card and the insurance paperwork instead.
- Sports. Broadcasts label teams by city, not by state, so you see PHI and PIT in a box score rather than PA.
- Crosswords. Setters clue it as Keystone State abbreviation, or as the state of Phila., with the shortened city in the clue signalling a shortened answer.
- International forms. ISO 3166 gives PA to Panama, so a shipping form that expects a country code will read your state as a different continent.
Learn the codes by playing
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