County lookup by address

When you need it

Mailing addresses don’t list the county, and the city in an address is often just the post office name. But a lot depends on the county: the sales tax on an order, property records and tax bills, voter registration, which court a case goes to, building permits, and many insurance and shipping quotes.

It’s also worth checking before you rent or buy. Two homes with the same city name and ZIP code can be in different counties, with different property tax rates and services.

The example is the White House: Washington, D.C. isn’t in any state or county, so the Census treats the District of Columbia as both.

Addresses we checked

We placed these addresses with the Census Bureau’s geocoder and then checked the point with TIGERweb, the same boundary service this tool uses, on October 31, 2026. The “city” in each address isn’t always the city the address is really in:

Caesars Palace, Washington University in St. Louis, Emory University, Kansas City International Airport and the Arlington County government building, respectively.

The St. Louis row is a classic: the address says “St. Louis”, but it’s in St. Louis County (FIPS 29189), outside any city, while the City of St. Louis is a separate, independent county equivalent (FIPS 29510). Most of Atlanta is in Fulton County, but Emory is in the DeKalb County part of the city.

How it works

We look up the address with Photon, a geocoder built on OpenStreetMap, and put a pin on the map. Then we check which county that point falls in using the Census Bureau’s official TIGER boundaries, the same ones federal agencies use. You also get the city (or “Unincorporated area”), the ZIP code area, the state and the coordinates.

The county is only as good as the pin. If the address has no house number, we place it in the middle of the street, and a long road can cross a county line. If the pin lands in the wrong spot, drag the map and tap the right building instead: the tool checks any point you tap.

Roads that are county or state lines

Some streets are the line itself. In Kansas City, State Line Road splits two states and two counties: a point at 39.0500, -94.6085 is in Wyandotte County, Kansas, and one at 39.0500, -94.6070, about 425 feet east, is in Jackson County, Missouri. Many rural roads are literally named County Line Road for the same reason.

For addresses on roads like these, the house number decides the side of the street, so always type it, and check the outline on the map to see which side of the line the pin is on.

Tips for typing an address

• House number first, then the street: “201 Dowman Dr, Atlanta”. Abbreviations like St, Ave, Blvd and NW work.
• Add the city or the ZIP code to tell apart streets with the same name in different towns.
• Apartment and suite numbers don’t change the county, so you can leave them out.
• A P.O. box isn’t a place, so it has no county: use the street address of the building instead.
• Brand-new subdivisions can take a while to appear in OpenStreetMap. If yours is missing, search the nearest main road and tap your lot on the map.