v t e Municipalities and communities of St. Clair County, Illinois, United States
County seat: Belleville
Cities	Belleville Cahokia Heights Collinsville‡ Columbia‡ East St. Louis Fairview Heights Lebanon Madison‡ Mascoutah O'Fallon	Map of Illinois highlighting St. Clair County
Villages	Brooklyn Caseyville Dupo East Carondelet Fairmont City‡ Fayetteville Freeburg Hecker‡ Lenzburg Marissa Millstadt New Athens New Baden‡ Sauget Shiloh Smithton St. Libory Summerfield Swansea Washington Park
Townships	Canteen Caseyville Centreville Engelmann Fayetteville Freeburg Lebanon Lenzburg Marissa Mascoutah Millstadt New Athens O’Fallon Prairie du Long Shiloh Valley Smithton St. Clair Stites Stookey Sugarloaf
CDPs	Darmstadt Floraville Paderborn Rentchler Scott AFB
Other unincorporated communities	Birkner Douglas Imbs North Dupo State Park Place‡ Westview Signal Hill
Footnotes	‡This populated place also has portions in an adjacent county or counties
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