St. Clair County is the oldest county in Illinois; its western border is formed by the Mississippi River, bordering Missouri. It is a part of the Metro East in southern Illinois. According to the 2020 United States Census, it had a population of 257,400, making it the eighth-most populous county in Illinois and the most populous in the southern portion of the state. Its county seat is Belleville. The county was founded in 1790 by the government of the Northwest Territory, from the western half of Knox County, before the establishment of Illinois as a state as the base for the Illinois Territory. Cahokia Village in the county was founded in 1697 and was a French settlement and former Jesuit mission.
Shiloh is a village in St. Clair County, Illinois, United States. The 2010 census recorded a population of 12,651. Shiloh is located within the St. Louis metropolitan area
Caseyville Township is located in St. Clair County, Illinois, United States. As of the 2010 census, its population was 31,996 and it contained 14,054 housing units.
Engelmann Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 726 and it contained 288 housing units.
Fayetteville Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 1,668 and it contained 722 housing units.
Freeburg Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 5,109 and it contained 2,118 housing units.
Lebanon Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 4,538 and it contained 2,005 housing units.
Lenzburg Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 1,047 and it contained 450 housing units.
Marissa Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 2,468 and it contained 1,175 housing units.
Mascoutah Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 8,217 and it contained 3,335 housing units.
Millstadt Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 6,718 and it contained 2,782 housing units.
New Athens Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 2,657 and it contained 1,129 housing units.
O'Fallon Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 26,053 and it contained 10,338 housing units.
Smithton Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 4,275 and it contained 1,684 housing units.
St. Clair Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 35,498 and it contained 15,366 housing units. St. Clair Township formed from a portion of Belleville Township on October 5, 1885.
Stites Township is located in St. Clair County, Illinois. As of the 2010 census, its population was 749 and it contained 326 housing units. Stites Township was originally named Brooklyn Township when it was reorganized from a portion of East St. Louis Township in February, 1888. Its name was changed to Stites in April, 1888.
Casner Township is one of sixteen townships in Jefferson County, Illinois, USA. As of the 2010 census, its population was 1,239 and it contained 510 housing units.
Field Township is one of sixteen townships in Jefferson County, Illinois, USA. As of the 2010 census, its population was 1,468 and it contained 637 housing units.
Grand Prairie Township is one of sixteen townships in Jefferson County, Illinois, USA. As of the 2010 census, its population was 909 and it contained 391 housing units.
Rome Township is one of sixteen townships in Jefferson County, Illinois, USA. As of the 2010 census, its population was 1,669 and it contained 771 housing units.
United States 
Illinois 
St. Clair 
