JoseFitani
📍 Geocoding & Lookup

County Finder

Enter any US address or coordinates to discover the county it falls within.

This page explains how the county finder works, the data and formulas behind it, and how to interpret the result. Geocoding is the foundation of every map application. Every time you search for a place in Google Maps, you are using a geocoder. Nominatim is the open-source geocoder from OpenStreetMap, free and covering the entire world. The tool is one of 329 free, open tools on JoseFitani for maps and geography. It runs in your browser with no sign-up needed. Use the search field or click the map to drop a pin - the tool uses Nominatim reverse geocoding on OpenStreetMap data and returns the result in seconds. Below you'll find a step-by-step guide, real use cases, the methodology, FAQs, and data sources.

Click anywhere on the map to get its coordinates and the nearest address (reverse geocoded via OpenStreetMap).

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How to use this tool

1
Enter your input

Type your query, paste coordinates, or click on the map. The tool uses Nominatim reverse geocoding on OpenStreetMap data to process your input locally in the browser.

2
View the result

The result appears instantly with the map showing your location. You can adjust by clicking elsewhere or searching a new place.

3
Copy or share

Click Copy to save to clipboard, or Share to send a direct link with the exact inputs.

What people use this tool for

Voter registration address

US voter registration runs through the county, so new residents must name theirs correctly. Entering a street address returns the county plus its FIPS code for the form. That beats guessing between neighbouring counties on a metro fringe.

Example: A newcomer to Austin enters her apartment address and confirms she is in Travis County before filling out the Texas voter registration form.
Court filing venue

Lawsuits generally get filed in the county where the defendant lives or the events occurred. Looking up the address pins down the right county courthouse before paperwork starts. Filing in the wrong county costs weeks and refiling fees.

Example: A small-claims filer in Los Angeles checks a business address and confirms it sits in Los Angeles County, not neighbouring Orange County.
Property tax lookup

Property tax records, assessor maps, and payment portals are all organised by county. Finding the county first points you to the right assessor's website. The FIPS code also helps when a tax tool asks for a numeric county identifier.

Example: A buyer eyeing a house in Phoenix looks up the county to reach the Maricopa County assessor's parcel search directly.
Genealogy record searches

Birth, marriage, and death records in the US are held at the county level, often going back centuries. Researchers tracing an ancestor's address need the county to know which archive to query. Boundary changes over time add a wrinkle the FIPS code helps untangle.

Example: A genealogist locates a 1920s family address in Brooklyn and confirms it falls in Kings County for the archive request.

How it's calculated

Uses reverse geocoding with administrative boundary data.

The calculation runs in your browser - no data is sent to our servers. Map tiles come from OpenStreetMap (ODbL license), geocoding uses Nominatim (1 request/second limit), and elevation uses the Open-Elevation API backed by SRTM data. All are free, open services.

All calculations use the WGS84 datum (EPSG:4326), the same as GPS. For other datums (NAD27, NAD83, ETRS89), a separate conversion is needed. The difference is typically under 1 metre - negligible for most uses but important for survey-grade work.

The formulas match those in professional GIS software (QGIS, ArcGIS, Global Mapper), just in a browser-friendly form. For sub-metre accuracy, use professional software with ellipsoidal calculations. Results are shown in multiple units: km and miles for distance, km²/m²/hectares/acres for area, metres and feet for elevation. Conversion factors are exact (1 mile = 1.609344 km), so the only error source is input precision.

Related tools and resources

For more tools in this category, explore the related tools listed below. Each tool includes full documentation, examples and FAQs. Explore related tools in our Geocoding category for complementary functionality. See the Tools index for all 329 tools, or read our blog for in-depth articles on geography and maps.

Frequently asked questions

Does this work outside the US?

County equivalents (provinces, departments) are supported in many countries.

What is a FIPS code?

It is the Federal Information Processing Standards numeric code that uniquely identifies every US county. The five-digit form combines a two-digit state code with a three-digit county code, for example 06037 for Los Angeles County. Government datasets and many tax tools use it as the canonical county identifier.

Does the county lookup work without internet?

Yes. Matching an address or coordinates to a county requires boundary data served over the network, so lookups fail offline. Each search sends your input to the lookup service and returns the containing county. Batch your lookups before heading somewhere without signal.

How accurate is the county match near borders?

The lookup tests your point against official county boundary polygons, so it is exact for the coordinates you supply. Accuracy therefore depends on the address geocoding: a rural route address that geocodes to the wrong side of a county line returns the wrong county. When a result looks surprising near a border, verify the pin position.

Why does Louisiana show parishes instead of counties?

Louisiana divides itself into parishes rather than counties, a legacy of its French and Spanish colonial administration. Alaska similarly uses boroughs and census areas. The finder returns the correct local equivalent wherever you search, because the underlying data follows each state's own terminology.

What about independent cities like in Virginia?

Virginia's independent cities are separate from any county, and the lookup reflects that: it returns the city itself with its own FIPS code. Baltimore, St. Louis, and Carson City are other independent cities treated the same way. The tool does not force a county where none exists.

Can I look up a county from coordinates alone?

Yes, dropping a pin or pasting latitude and longitude works just as well as typing an address. The point-in-polygon test only needs the location, not a street name. This is handy for rural land, trailheads, and lake houses with vague addresses.

Do county boundaries ever change?

Rarely, but it happens: new counties are occasionally carved out of existing ones, most recently in fast-growing western states. The boundary dataset behind the lookup is updated as changes take effect. For historical research, always check which county existed at the date you care about.

Is the result an official legal determination?

No. The finder is a convenient lookup, not a legal authority on jurisdiction. For court filings, tax liability, or voting eligibility, confirm with the county clerk or assessor. Boundary datasets are excellent but a clerk's answer is the one that counts in a dispute.

Data sources & methodology