Belleville (French: Belle ville, meaning "Beautiful city") is a city and the county seat of St. Clair County, Illinois, coterminous with the now defunct Belleville Township. It is also the seat of the Roman Catholic Diocese of Belleville and the National Shrine of Our Lady of the Snows. The population was 44,478 according to the Census Bureau's 2010 data, making it the largest city in the state south of Springfield.
Belleville is the eighth-most populated city in the state outside the Chicago metropolitan area, and the most-populated city in southern Illinois and in the Metro-East region of the St. Louis Metropolitan Area. Due to its proximity to Scott Air Force Base, the population receives a boost from military and federal civilian personnel, defense contractors, and military retirees.