What is my ZIP code?

ZIP codes and ZCTAs

ZIP codes are mail delivery routes, not areas, so the Postal Service doesn’t publish boundaries for them. The Census Bureau builds the closest thing, ZIP Code Tabulation Areas (ZCTAs), from the ZIP codes of the addresses in each census block. They match the mailing ZIP code almost everywhere, and that’s what we show and draw.

Some ZIP codes have no area at all: P.O. boxes, single buildings and big organizations often get their own. The example, the Empire State Building, has a ZIP code all to itself (10118), but that ZIP has no ZCTA, so the map shows the area around it: 10001.

ZIP codes we looked up

We checked these spots with TIGERweb, the Census service the tool uses, on October 31, 2026. The ZIP on the mail comes from the Census Bureau’s address geocoder:

Residents and land area of each ZCTA: Census 2025 Gazetteer Files and American Community Survey 2020–2024 estimates.

ZIP codes by the numbers

The Census data behind the tool has 33,642 ZCTAs in the 50 states and D.C. A few of them stand out:

• The most populated is 77494, in Katy, Texas, west of Houston, with 140,157 residents in the 2020–2024 estimates.
• The largest is 99557, around Lime Village in Alaska: 13,680 square miles of land, more than the whole state of Maryland.
• The smallest cover about 0.01 square miles, a single block or tower, like 19108 in Philadelphia.
• 599 ZCTAs have no residents at all: business districts, airports, parks and places like Kennedy Space Center.

Puerto Rico has ZCTAs too, starting with 00: Old San Juan is 00901, and the tool shows it.

How the five digits work

ZIP codes were introduced in 1963. The first digit is a group of states, from 0 in the Northeast (plus Puerto Rico) to 9 on the West Coast, Alaska and Hawaii. The first three digits are the mail processing center that sorts the area’s mail, and the last two narrow it down to a post office or delivery zone. ZIP+4 adds four more digits for a block, a building or even one company.

That’s why neighboring towns can share a ZIP code and a big city has dozens, and why a ZIP code doesn’t tell you the city or the county reliably.

From your location or an address

Use your location and we look up the ZCTA you’re standing in. Type an address and we place it on the map first, then do the same. You’ll also get the nearest street address, the city (or “unincorporated”), the county and the state. Short distances, like your GPS accuracy, are shown in feet and miles.

Near the edge of a ZIP code area, especially in rural places, the two sides of a road can have different ZIP codes. When it matters, for shipping or a form, use the ZIP code on your mail.

When there’s no ZIP code

ZCTAs only cover land with addresses, so mountaintops, deserts and open water usually have none: Mauna Kea, Badwater Basin in Death Valley and the middle of the Golden Gate Bridge all came back without one. And ZIP codes ignore state lines: at the Four Corners, ZCTA 86514 (Teec Nos Pos, Arizona) covered our test points in Utah, New Mexico and Arizona, while the Colorado one had no ZCTA at all.