CITY · CO

What county is Boulder, CO in?

Boulder, CO is mostly in Boulder County. County FIPS code 08013, population 326,831 (2023 estimate).

County details

City: Boulder, Colorado
Primary county: Boulder County
FIPS code: 08013
County population: 326,831

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

Questions

What county is Boulder in?

Boulder, CO is mostly in Boulder County.

What is the county seat of Boulder 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.