St. Clair County, Illinois facts for kids
|St. Clair County, Illinois|
Location in the state of Illinois
Illinois's location in the U.S.
674 sq mi (1,746 km²)
658 sq mi (1,704 km²)
16 sq mi (41 km²), 2.4%
411/sq mi (159/km²)
|Time zone||Central: UTC-6/-5|
|Named for: Arthur St. Clair|
St. Clair County is the oldest county in the U.S. state of Illinois. According to the 2010 census, it had a population of 270,056, making it the eighth-most populous county in Illinois and the most populous in the southern part of the state. Its county seat is Belleville. The county was founded in 1790, before the establishment of Illinois as a state.
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St. Clair County, Illinois Facts for Kids. Kiddle Encyclopedia.