CITY · DE

What county is Wilmington, DE in?

Wilmington, DE is mostly in New Castle County. County FIPS code 10003, population 578,592 (2023 estimate).

County details

City: Wilmington, Delaware
Primary county: New Castle County
FIPS code: 10003
County population: 578,592

Some cities extend into more than one county. Wilmington is placed in the county that contains its center. For a specific address, use the address lookup.

Questions

What county is Wilmington in?

Wilmington, DE is mostly in New Castle County.

What is the county seat of New Castle County?

County seats are not part of the data on this site. Check the county’s official website.

Can a city be in two counties?

Yes. Large cities such as Houston and Atlanta cross county lines. The address lookup shows the exact county for any street address.

Sources: U.S. Census Bureau geographic reference files; FCC Area API; Census Bureau Population Estimates, Vintage 2023. Last reviewed 2026-10-27.