Cahokia is a settlement and former village in St. Clair County, Illinois, United States, founded as a colonial French mission in 1689. Located east of the Mississippi River in the Greater St. Louis metropolitan area, as of the 2010 census, 15,241 people lived in the village. On May 6, 2021, the village was incorporated into the new city of Cahokia Heights.

St. Clair County is the ninth most populous county in Illinois. Located directly east of St. Louis, the county is part of the Metro East region of the Greater St. Louis metropolitan area in southern Illinois. As of the 2020 United States census, St. Clair County had a population of 257,400, making it the third most populous county in Illinois outside the Chicago metropolitan area. Belleville is the county’s seat and largest city.