ZIP Codes: The First Digit Tells You the Region
A letter arrives with the ZIP code 90210. Before you read the street, before you read the city, the first digit has already told you something: this letter is going to the far West. A ZIP code starting with 0 is going to the Northeast. One starting with 5 is going to the Upper Midwest. The first digit of a ZIP code is a compass — it runs 0 in the Northeast to 9 in the far West, and it names the region before the rest of the code names anything at all. This guide walks the digits from 0 to 9, state by state, explains the one big exception that catches everybody, and shows how to read a ZIP code the way a mail sorter reads it — so the next time a five-digit code flashes past, you know the region before you know the town.
The First Digit Runs East to West
ZIP codes were launched nationwide on 1 July 1963 — ZIP stands for Zone Improvement Plan — and the first digit was designed as a map. The country was divided into ten regions, numbered 0 to 9 from east to west, and every ZIP code in the country starts with the digit of its region. Digit 0 is the Northeast: Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut and New Jersey. Digit 1 is New York, Pennsylvania and Delaware. Digit 2 is the District of Columbia, Maryland, Virginia, West Virginia, North Carolina and South Carolina. Digit 3 is the Southeast: Georgia, Florida, Alabama, Tennessee and Mississippi. Digit 4 is the Great Lakes: Ohio, Michigan, Indiana and Kentucky. Digit 5 is the Upper Midwest: Iowa, Minnesota, Montana, North Dakota, South Dakota and Wisconsin. Digit 6 is the Central Plains: Illinois, Kansas, Missouri and Nebraska. Digit 7 is the South Central: Arkansas, Louisiana, Oklahoma and Texas. Digit 8 is the Mountain West: Arizona, Colorado, Idaho, New Mexico, Nevada, Utah and Wyoming. Digit 9 is the far West: Alaska, California, Hawaii, Oregon and Washington. Learn the two ends — 0 Northeast, 9 far West — and the middle — 5 Upper Midwest — and the other seven digits fall between them in order.
| Digit | Region | States |
|---|---|---|
| 0 | Northeast | ME, NH, VT, MA, RI, CT, NJ |
| 1 | New York, Pennsylvania, Delaware | NY, PA, DE |
| 2 | Mid-Atlantic & Southeast | DC, MD, VA, WV, NC, SC |
| 3 | Southeast | GA, FL, AL, TN, MS |
| 4 | Great Lakes | OH, MI, IN, KY |
| 5 | Upper Midwest | IA, MN, MT, ND, SD, WI |
| 6 | Central Plains | IL, KS, MO, NE |
| 7 | South Central | AR, LA, OK, TX |
| 8 | Mountain West | AZ, CO, ID, NM, NV, UT, WY |
| 9 | Far West | AK, CA, HI, OR, WA |
Notice what the table does not do: no digit belongs to a single state. Digit 1 covers three states, digit 3 covers five, digit 0 covers seven. The first digit is a region key, not a state key — and that is the first thing most people get wrong about ZIP codes. The second and third digits narrow it to a region within the state, and the last two name the post office or the delivery area. So a ZIP code is a zoom: the first digit is the country cut into ten strips, and each later digit zooms in one level further.
The Mail-Route Exception
Here is the exception that catches everybody: ZIP codes follow mail routes, not state borders. A single post office can serve addresses across a county line, and rarely across a state line — so one ZIP code can cover ground in two states. Fort Campbell, the army post on the Kentucky–Tennessee line, uses 42223 for addresses on both sides of the border. A ZIP in the Oregon–California border country, 97635, serves addresses in both states. The rule is not “every ZIP starting with 0 is in New England” as an absolute — it is “mostly, generally”, because the mail route is what matters and the state line is not. That is why the quiz never asks “which state is this ZIP code in?” with a digit alone: the digit names the region, and the region is the honest answer. Any question that pretends a ZIP digit proves a state is a bad question, and this quiz does not ask it.
00501 — The Lowest ZIP in Use, and the Missing 00000
The lowest ZIP code in use is 00501, and it belongs to the IRS processing centre in Holtsville, New York. It starts with two zeroes because it sits at the very bottom of the Northeast range, and it is a useful anchor: if a question offers 00001 or 00000 as the lowest ZIP, both are wrong, because there is no 00000 and no 00001 in use. The numbering starts at 00501, not at zero, because the first digit 0 was assigned to the Northeast and the first three digits 005 were assigned to the New York area — and the last two digits, 01, are the post office. Famous ZIP codes work the same way: 90210 is Beverly Hills, California, because 9 is the far West and 902 narrows it to southern California; 10001 is New York City, because 1 is New York and 100 narrows it to Manhattan. Once you know the first digit, the famous codes stop looking random — 90210 could never be in Maine, and 00501 could never be in California, because the first digit says so before the rest of the code says anything.
How to Remember the Digits
Do not try to memorise fifty states by ZIP digit. Memorise ten regions in order, west to east in reverse: 0 Northeast, 1 New York–Pennsylvania–Delaware, 2 Mid-Atlantic and Southeast, 3 Southeast, 4 Great Lakes, 5 Upper Midwest, 6 Central Plains, 7 South Central, 8 Mountain West, 9 far West. Say them as a chant — “zero Northeast, nine far West, five Upper Midwest” — and the rest fill in between. Then anchor each digit with one famous ZIP: 00501 Holtsville for 0, 10001 Manhattan for 1, 90210 Beverly Hills for 9. Then play the quiz: twenty rounds, ten seconds each, area codes and ZIP digits in separate rounds, and every miss comes back with the fact that explains it — the region the digit names, the overlay that changed the list. One game a day is enough. The digits do not change, the regions do not change, and the second game is almost always better than the first, because the first digit is already half-memorised by the time the timer runs out.
What does the first digit of a ZIP code mean?
The region, east to west: 0 is the Northeast and 9 is the far West. It names a region, not a state — no digit belongs to a single state.
Can a ZIP code cross a state line?
Yes. ZIP codes follow mail routes, not state borders — Fort Campbell uses 42223 for addresses in both Kentucky and Tennessee, and 97635 serves both Oregon and California.
What is the lowest ZIP code in use?
00501, the IRS centre in Holtsville, New York. There is no 00000 and no 00001 in use.
When were ZIP codes introduced?
1 July 1963, as the Zone Improvement Plan. Area codes came earlier, in 1947.
One digit, ten regions, and a compass built into every address in the country. The first digit is the region, the last four are the zoom, and the mail route — not the state line — is what the code actually follows. Test yourself on all of it now, area codes and ZIP digits included. And if you want to practise the states themselves — not just their codes — the free us states quiz map game is the best place to do it.