St. Charles County

Also known as St. Charles County, Missouri, Saint Charles County, Missouri, St. Charles County, MO

county in Missouri, United States

Key facts

Country: United States
State: Missouri
Founded: October 1, 1812
Named after: Charles Borromeo
Seat: St. Charles
Largest city: O'Fallon
County executive: Steve Ehlmann ( R )
Total: 593 sq mi (1,540 km )
Land: 560 sq mi (1,500 km )
Water: 32 sq mi (83 km ) 5.4%
Estimate 2025: 426,499
Density: 720/sq mi (280/km )
Time zone: UTC−6 ( Central )

Article

St. Charles County is located in the central eastern part of the U.S. state of Missouri. As of the 2020 census, the population was 405,262, making it Missouri's third-most populous county. Its county seat is St. Charles. The county was organized October 1, 1812, and named for Saint Charles Borromeo, an Italian cardinal.

St. Charles County is part of the St. Louis, MO-IL Metropolitan Statistical Area and contains many of the city's northwestern suburbs. The wealthiest county in Missouri, St. Charles County is one of the nation's fastest-growing counties.