Cahokia is a village in St. Clair County, Illinois, United States. It is part of Greater St. Louis, the metropolitan area around St. Louis. As of the 2010 census, the village had a population of 15,241, a decline from 16,391 in 2000. The name is a reference to one of the clans of the historic Illini confederacy, who were encountered by early French explorers to the region.