How to Find Out What County You Live In (and What County an Address Is In)

To find out what county you live in, look up your exact location or street address against county boundaries. On a phone, open What County Am I In at home and allow location access; it tests your GPS position against county boundaries and also tells you how far the nearest county line is. If the result is close to a line, confirm it with your property tax bill or county assessor.

Each method has a different strength:

The U.S. Census Bureau's free Census Geocoder is the official option for addresses. Choose "Find Geographies", enter a one-line address, and it returns the matched location with its state, county, census tract and block, including the county's FIPS code. It can also process up to 10,000 addresses in one batch file, which is useful for a mailing list or a spreadsheet.

A map works too. The interactive US county map lets you click your area and read the county name, and the map with county lines draws county boundaries over streets so you can see which side of a line your house is on.

Many people check their county by typing a 5-digit ZIP code into a search engine. This often produces a wrong or incomplete answer, because ZIP codes are not geographic land areas. The Post Office Department launched ZIP Codes on July 1, 1963, to speed up mail sorting, and the Postal Service still assigns them to delivery routes and post offices, not to counties.

A substantial share of ZIP codes cross county lines, and a few even cross state lines. Two houses with the same ZIP code can sit in different counties, pay property tax to different assessors and vote in different elections. ZIP-to-county lists usually assign each ZIP to the county where most of its addresses fall, which is fine for rough statistics and wrong for the households on the other side of the line.

The reliable automated method is to start from a location (a GPS fix or a geocoded address) and test which county polygon contains it. You can see how ZIP areas and counties overlap by checking your ZIP with the ZIP code lookup and comparing the result with your county.

Every county lookup tool, including the ones on this site, follows the same basic recipe:

1. Get a coordinate. Either your device reports a latitude and longitude, or an address is converted to coordinates by a geocoder.
2. Run a point-in-polygon test. The coordinate is checked against county boundary polygons. The polygon that contains the point is your county.
3. Report the result and its uncertainty. A good tool also tells you how far the point is from the nearest county line, because that distance tells you how much to trust the answer.

On Open Map Lab the polygons are the U.S. Census Bureau's generalized cartographic boundary files (2017 edition, 1:10,000,000 scale), bundled with the site and tested in your browser. Generalized means the lines have been simplified for small-scale mapping: they are excellent for telling which county a house in the middle of a county belongs to, but they can differ from the legal line by hundreds of meters in places, especially along winding rivers and irregular survey lines.

The Census Bureau also publishes full-resolution boundaries in its TIGER/Line files, and many counties publish their own parcel-level GIS layers. Those are the sources to consult when the answer has legal or financial consequences.

To find the county for an address you are not standing at, such as a house you are buying, a client's office or a relative's home:

1. Enter the full street address in the address to county lookup: house number, street, city or ZIP, and state. A street name alone or a ZIP code alone gives the geocoder too little to work with.
2. Check the pin. The address is converted to coordinates first. Zoom in and make sure the pin sits on the right building, not at the middle of the street, the ZIP code's center or a different town with the same street name.
3. Read the county and the distance to the line. The tool tests the pin against county boundaries and reports the county, state and how far the nearest county line is. A distance of a few miles means the answer is solid.
4. If the line is close, cross-check. Run the same address through the Census Geocoder, then open the county assessor's parcel search for the county you got. If the parcel is listed there, you have your answer.
5. Near a state line, check the state too. County lines often double as state lines, so confirm the state with What State Am I In, which also reports the distance to the nearest state border.

The mailing city in the address is not evidence of the county. The Postal Service names the delivering post office, which can be in a neighboring county or the address can be outside any city at all. Counties and cities are separate layers; to check if you're inside city limits, use the city finder, and see What Is a Census Designated Place? for how unincorporated communities fit in.

If the reported distance to the nearest boundary is small, treat the result as a strong hint rather than a final answer and confirm it with an official source.

Federal statistical standards count "counties and equivalent entities", because several states organize local government differently:

1. Virginia independent cities: Virginia has 38 independent cities (for example Alexandria, Richmond and the City of Fairfax) that are not part of any county. Each is its own county equivalent with its own FIPS code, so a lookup can correctly return a city rather than a county.
2. Louisiana parishes: Louisiana is divided into 64 parishes, a name inherited from its French and Spanish colonial history. Parishes function as counties for federal statistical purposes.
3. Alaska boroughs and census areas: Alaska has organized boroughs plus a large Unorganized Borough that has no county-level government. The Census Bureau divides the unorganized area into census areas purely for statistics.
4. Connecticut planning regions: Connecticut abolished county government in 1960. Starting with 2022 data products, the Census Bureau uses the state's 9 planning regions as county equivalents instead of the 8 historic counties. Note that this site's boundary files are the 2017 edition, which still show the 8 historic counties for Connecticut.

Other county equivalents include the independent cities of Baltimore, St. Louis and Carson City, the District of Columbia, and Puerto Rico's municipios. Consolidated city-counties such as San Francisco and Denver are single entities that act as both city and county.

Two separate uncertainties stack up near a boundary:

• Position error. A phone outdoors with a clear sky is often accurate to within several meters, but indoors or in a dense downtown the error can grow to tens of meters, and a desktop computer may be off by miles if it falls back to IP geolocation. See How GPS Location Accuracy Works.
• Boundary error. Generalized boundary lines are simplified versions of the legal line, so even a perfect coordinate can land on the wrong side when it is very close to the border.

When boundary precision matters for property taxation, voter registration, jury summons, building permits or school enrollment, look up your parcel number in the county assessor's or county GIS office's records. Those offices maintain the authoritative parcel and jurisdiction data, and the assessor's record of which county taxes your parcel is what governs.

Most county mix-ups come from treating a convenient label as a jurisdiction:

• Trusting the mailing city. Your postal city is the name of the delivering post office. It can belong to a city in a different county or to no city at all.
• Assuming you live in a city. Many addresses are in unincorporated areas governed directly by the county, even though the mailing address names a nearby town.
• Using the school district or utility as a proxy. School districts, fire districts and water districts often cross county lines.
• Relying on a ZIP-to-county table. These tables usually pick one county per ZIP.

When sources disagree, use the one that is responsible for the decision you care about: