County Lookup: What County Is a ZIP Code In?
Find the county a ZIP code is in, or the counties it spans (a ZIP is a postal route, not a county), plus the single county for any street address. ZIP mapping uses the federal HUD-USPS crosswalk; addresses use official U.S. Census boundaries.
- Street address
- City or place
- ZIP code
ZIP code or street address:
How to look up a county
- Enter a ZIP code or a street address. Type a 5-digit ZIP code to see every county it touches, or a full street address to get the one county that address is in.
- We match it to the authoritative source. A ZIP is matched against the federal HUD-USPS ZIP-County crosswalk (built from USPS delivery data); an address is matched against the Census Bureau’s official TIGER county boundaries.
- See the county (or counties) and their share. A ZIP shows each county it reaches with the share of its residential addresses there; an address shows its single county with population, income, and unemployment.
Why one ZIP code can span two or more counties
The Postal Service draws ZIP codes to move mail efficiently along carrier routes, which follow roads and delivery density rather than county lines. Where a carrier route crosses a county boundary, the ZIP crosses with it, so the same five digits can deliver to addresses in two, three, or more counties. In the current HUD-USPS crosswalk, 11,379 of 39,484 ZIP codes touch more than one county. That is why a ZIP-based lookup returns a set of counties with each one’s share, while an address-based lookup can return the single, exact county.
ZIP code vs. ZCTA: why the two give different answers
There are two different things people call a “ZIP,” and confusing them produces wrong answers. The postal ZIP is the USPS delivery construct above. A ZCTA (ZIP Code Tabulation Area) is something else: a polygon the Census Bureau draws to approximate a ZIP, by assigning each census block to the ZIP most of its addresses use. ZCTAs are handy for statistics, but they are a re-drawing, and they don’t always match where the mail goes.
ZIP 10505 (Baldwin Place, New York) is the textbook case. HUD’s postal crosswalk puts 60% of its residential addresses in Putnam County and 40% in Westchester County. But the 2020 Census ZCTA for 10505 lies entirely inside Westchester. So a tool built on ZCTA boundaries names the wrong primary county. HUD-USPS 2026 Q2 · Census TIGER ZCTA 2020 This lookup uses the postal (HUD-USPS) mapping, so it returns both counties in the order the mail favors.
Common questions
Can one ZIP code be in more than one county?
Yes. 11,379 ZIP codes span two or more counties in the 2026 Q2 crosswalk, because ZIPs follow postal delivery routes rather than county boundaries. Enter the ZIP above to see each county it reaches and the share of its addresses there.
What county is ZIP 10505 in?
ZIP 10505 (Baldwin Place, New York) spans two counties: 60% of its residential addresses are in Putnam County and 40% in Westchester County (HUD-USPS, 2026 Q2). The 2020 Census ZCTA for 10505 lies inside Westchester alone, so ZCTA-based answers name only Westchester.
Is a ZIP code the same as a county?
No. A ZIP code is a postal delivery route owned by USPS; a county is a unit of government with its own courts, elections, property records, and taxes. A ZIP can sit inside one county, cross several, and occasionally cross a state line. That is why the county has to be looked up, not assumed.
What is a county FIPS code?
Every U.S. county has a 5-digit FIPS/GEOID: a 2-digit state code plus a 3-digit county code. Putnam County, New York is 36079; Westchester County is 36119. Each county in the results above shows its FIPS code.
Sources
- Source: U.S. Department of Housing and Urban Development, HUD-USPS ZIP–County Crosswalk, 2026 Q2 — retrieved Nov 2026
- Source: U.S. Census Bureau, Census Geocoder, current benchmark and vintage — retrieved Nov 2026
- Source: U.S. Census Bureau, TIGERweb county boundaries, January 1, 2026 vintage — retrieved Nov 2026