St. Clair County, Illinois

St. Clair County
St. Clair County Courthouse in Belleville
Location within the U.S. state of Illinois
Illinois's location within the U.S.
Coordinates: 38°28′N 89°56′W / 38.47°N 89.93°W / 38.47; -89.93
Country United States
State Illinois
Founded1790
Named forArthur St. Clair
SeatBelleville
Largest cityBelleville
Area
 • Total674 sq mi (1,750 km2)
 • Land658 sq mi (1,700 km2)
 • Water16 sq mi (40 km2)  2.4%
Population
 • Total257,400
 • Density380/sq mi (150/km2)
Time zoneUTC−6 (Central)
 • Summer (DST)UTC−5 (CDT)
Websitewww.co.st-clair.il.us

St. Clair County is the oldest county in the U.S. state of Illinois. According to the 2020 census, it had a population of 257,400,[1] making it the ninth-most populous county in Illinois. Its county seat is Belleville.[2] The county was founded in 1790, before the establishment of Illinois as a state.

References

  1. 1.0 1.1 "QuickFacts: St. Clair County, Illinois". United States Census Bureau. Retrieved August 14, 2023.
  2. "Find a County". National Association of Counties. Retrieved 2011-06-07.