St. Clair County Map, Illinois

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St. Clair County, Illinois

St. Clair County sits right across the Mississippi River from St. Louis. Belleville, the county seat, is the largest city. It’s a place of contrasts. You’ve got urban grit and rural areas. But there’s also blue-collar neighborhoods and upscale suburbs.

St. Clair County feels like a blend of Midwest and Gateway City. It’s complex, diverse, and always evolving. East St. Louis has seen tough times, but there’s resilience here. The county has deep roots. It was founded in 1790, making it one of the oldest in Illinois.

The landscape varies from Mississippi River floodplain to rolling hills. Scott Air Force Base is a major employer and shapes the local culture. You’ll see a lot of military folks around. The riverfront casino draws crowds. So does Cahokia Mounds, a UNESCO World Heritage site.

Category	Details
County Name	St. Clair County
County Seat	Belleville
Population	Approximately 265,000
Cities, Towns, and Communities	Belleville, East St. Louis, O’Fallon, Cahokia, Fairview Heights, Swansea, and several smaller communities
Interstates and Highways	Interstate 64, Interstate 55, Interstate 255, U.S. Route 50, U.S. Route 61, U.S. Route 40
FIPS Code	17-163
Total Area (Land and Water)	658 square miles (land: 657 sq mi, water: 1 sq mi)
Adjacent Counties (and Direction)	Madison County (North), Clinton County (Northeast), Washington County (East), Randolph County (South), Monroe County (Southwest), St. Louis, Missouri (West), St. Louis County, Missouri (West)
Time Zone	Central Time Zone (CT)
State	Illinois
Coordinates	38.5369° N, 90.0734° W
Etymology	Named in honor of Arthur St. Clair, a major general in the American Revolutionary War
Major Landmarks	The Gateway Arch, Cahokia Mounds, Belleville Historic District, and Scott Air Force Base