St. Clair County, Illinois

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 second most populous county in Illinois outside the Northern Third. Belleville is the county seat and largest city.