Address to County Lookup (Any US Address)
Type a US street address to look up the county, Louisiana parish or Alaska borough it belongs to, with the five-digit FIPS code, county seat and state on a map. For your current GPS position, use What County Am I In.
Ready to Lookup County by Address
Enter any street address, residential property, or postal code to determine the legal county jurisdiction, county seat, and FIPS code.
How to use the address to county lookup
- 1Type a US address
Enter a full street address; adding the ZIP code helps the geocoder.
- 2Geocode and match the county
The address is turned into coordinates and tested against Census county boundaries in your browser.
- 3Read the county and FIPS code
See the county, parish or borough, its FIPS code, county seat and state, confirmed on the map.
How to Find the County From an Address
Determining the precise county of an address is not a simple string match against a postal database. Street names are frequently shared across neighboring jurisdictions, and postal ZIP codes regularly overlap multiple counties. A robust county lookup tool must resolve an address into geodetic coordinates (latitude and longitude) and test that point against digital county boundary polygons.
Open Map Lab utilizes a multi-tiered lookup engine. First, address inputs are parsed and normalized to standardize street prefixes, suffixes, and directional cardinal tags. Second, the location is geocoded to its exact coordinate on the WGS84 ellipsoid. Finally, a spatial lookup matches the coordinate against U.S. Census Bureau county boundaries (generalized cartographic files, so results near a county line are approximate) to identify the jurisdiction, FIPS code, and administrative seat. If you have no address because you are on a highway or out in the country, you can find your state from GPS and then narrow it down to the county.
Which County Boundary Data Is Used?
The official source of civil and administrative boundaries in the United States is the Census Bureau’s Topologically Integrated Geographic Encoding and Referencing (TIGER) system. Open Map Lab uses the Census cartographic boundary files derived from it (2017 edition, generalized to 1:10,000,000), which are bundled with the site and tested in your browser. They are simplified, so a point within roughly a kilometer of a county line can land on the wrong side. These files define:
- County FIPS Codes: Five-digit Federal Information Processing Standards codes uniquely identifying every county (e.g.,
06037for Los Angeles County, CA). - County-Equivalent Entities: Parishes in Louisiana, organized boroughs and census areas in Alaska, and 38 independent cities in Virginia, plus Baltimore (MD), St. Louis (MO), and Carson City (NV).
- Connecticut’s Planning Regions: The replacement of historic county entities with regional Councils of Government (COGs) enacted in federal standards in 2022. The 2017 boundary file used here still contains the 8 historic counties, so Connecticut results show the legacy county.
Why Your Mailing Address Can Point to the Wrong County
More than 25% of all postal addresses in the United States list a “city” in their postal delivery address that does not correspond to the actual incorporated municipality or county where the home physically resides.
For instance, a homeowner might have a mailing address of “Los Angeles, CA” but reside in an unincorporated sector of Los Angeles County governed directly by the Board of Supervisors, or have a “Silver Spring, MD” address that spans across Montgomery County without an actual municipal charter.
How the County Match Is Calculated (Point in Polygon)
How your geocoded address is mathematically matched against complex county boundary polygons:
\text{Inside} = \left( \sum_{i=1}^{M} \text{Intersect}(R_{\text{ray}}, S_i) \right) \pmod 2 \equiv 1- Extract bounding box of New York County: [-74.0477, 40.6803] to [-73.9067, 40.8790]
- Point P falls inside bounding box. Proceeding to rigorous ray-casting.
- Iterate through 3,412 segments of Manhattan Island contour:
- Ray intersects East River boundary at Lon -73.9721° (Intersection 1 - odd)
- No further intersections detected eastward across Long Island sound in target bounds.
- Total intersections = 1 (odd number -> Point is INSIDE polygon).
Ray-casting evaluates exact geometric inclusion in sub-milliseconds, bypassing imprecise zip-code boundary approximations.
Examples: Addresses That Are Easy to Assign to the Wrong County
Examples of addresses where postal designations conflict with true county jurisdictions:
Cross-Jurisdictional Postal vs. County Discrepancies
Examples of postal and county mismatches; confirm any single address with the county assessor or recorder.
| Street Address | Mailing City | Actual County | FIPS Code | Geographic Anomaly |
|---|---|---|---|---|
| 1000 S Pokegama Ave | Grand Rapids, MN | Itasca County | 27061 | Spans unorganized territory boundaries |
| 1900 E 4th St | Charlotte, NC | Mecklenburg County | 37119 | Postal area overflows into Cabarrus County |
| 450 State St | Bristol, VA | Bristol (Independent City) | 51520 | Centerline of street marks Tennessee-Virginia border |
| 1500 Main St | Kansas City, MO | Jackson County | 29095 | Distinct from Wyandotte County, Kansas City, KS |
| 100 E Broadway | Long Beach, NY | Nassau County | 36059 | Independent city charter within suburban county ring |
Address to County Accuracy and Limitations (Legal, Tax, Property)
Review these guidelines when using automated county lookup tools:
- Property Tax & Deeds: County boundaries shown are based on Census Bureau statistical representations. For legal tax assessments, deed registrations, or zoning disputes, consult your local County Recorder or Tax Assessor.
- School Districts: School district lines frequently do not align with county borders. An address in one county may be zoned for schools in another.
- Emergency Response: 911 dispatch relies on Computer Aided Dispatch (CAD) systems tied directly to emergency service numbers (ESNs) rather than postal mailing addresses.
Related County & Location Tools
Use GPS to detect your current position with What County Am I In? or browse all jurisdictions on the Interactive US County Map.
Quick facts about the address to county lookup
| Fact | Value | Notes |
|---|---|---|
| Jurisdiction Coverage | All 50 US States & D.C. | Includes 38 Virginia Independent Cities |
| FIPS Coding | Federal Standard 5-Digit | 2-digit state + 3-digit county identifier |
| Legal Applications | Taxes, Permits, Jury Duty | Property deeds and court summons |
Edge cases and exceptions
Postal City vs. County Seat Mismatch
Your mailing address city often differs from your county seat. For example, a home in Silver Spring, MD is in Montgomery County (county seat Rockville).
The address to county lookup: worked examples
Property Tax Authority Verification
Scenario: Verifying tax jurisdiction for an address near the Dallas/Collin county border.
Outcome: Verifies the property parcel sits within Collin County (FIPS 48085) with county seat McKinney.
Frequently asked questions about the address to county lookup
How do I find out what county an address is in?
Enter the street address or ZIP code into the search bar. The tool resolves the exact geographic parcel location and matches it against US Census county boundary polygons (generalized 1:10,000,000).
Why does an address ZIP code not match the county?
ZIP codes are mail delivery routes designed by the USPS and regularly cross county and municipal boundaries.
Does an address always sit in the county shown in its mailing city?
No. A mailing city can span more than one county, so the county should be determined from the address location, not the city name.
How do I find the county for a PO Box?
A PO Box has no physical location, so it cannot be mapped to a county. Use the physical or residence address instead.
What is a Louisiana parish and how does the tool show it?
Louisiana's 64 parishes are the state's county-equivalents. The tool labels them as parishes and uses the same FIPS structure.
Which source defines the county for an address?
The address is converted to coordinates, then the county is read from OpenStreetMap administrative boundaries and matched to US Census records for the FIPS code, county seat and population where available. For legal matters the county assessor's parcel record is authoritative.
Can I look up many addresses at once?
This tool handles one address at a time. For a list, you can use the CSV to Map tool to plot coordinates and the county map to inspect each location.
What is the county FIPS code used for?
It is a five-digit code, two for the state and three for the county, used in federal data, tax tables, tax-rate lookups and disaster declarations.
Does the result show the county seat?
Yes. The county seat is displayed beside the county name and state.
What about addresses in an independent city?
The result will name the independent city, which is a county-equivalent not located inside any county.
How accurate is the address match?
Address matching uses OpenStreetMap data and is typically street-level or rooftop in cities, but can be approximate in rural areas. Check the returned location on the map.
Does it work for new construction?
Very new addresses may be missing from the geocoder. If so, search a nearby street or click the property on the map.
Keep exploring
What to do with this result
- What County Am I In?Use this to find out what county you are in.
- County Map With Cities, Towns & County SeatsUse this to view a county map with cities.
- Address to Coordinates Converter (Lat/Long & UTM)Use this to convert an address to coordinates.
- Map With County Lines (County Boundaries on a Street Map)Use this to show county lines on a street map.
- What ZIP Code Am I In?Use this to find your ZIP code.
Related map tools
Blog posts, studies & methodology
Printable blank maps
- Printable blank map libraryWorld, continent, US and state outline maps (PDF/PNG/SVG).
- Blank map: United States All Counties MapFree printable outline map.
- Blank map: United States with State BordersFree printable outline map.
- Blank map: United States with State CapitalsFree printable outline map.
- Blank map: United States OutlineFree printable outline map.
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