St. Clair County, Illinois
St. Clair County is a county in Illinois with an estimated population of 251,018 in 2023. 24 cities, towns and Census places in it are indexed here.
Largest places in St. Clair County
Belleville 40,726O'Fallon 31,968East St. Louis 17,642Cahokia Heights 17,114Fairview Heights 16,125Shiloh 14,736Swansea 14,472Mascoutah 8,916Lebanon 4,571Freeburg 4,501Caseyville 4,359Millstadt 3,943Smithton 3,900Dupo 3,821Washington Park 2,493Fairmont City 2,174New Athens 1,873Marissa 1,752Brooklyn 626St. Libory 610Lenzburg 451East Carondelet 375Summerfield 332Fayetteville 286
About St. Clair County
St. Clair County is one of the counties of Illinois. County governments in Illinois handle local services such as courts, property records and elections; cities and towns inside the county run their own municipal services. Population figures come from the Census Bureau's Vintage 2023 estimates, which are updated annually.