Belleville (French: Belle ville, meaning "Beautiful city") is a city in St. Clair County, Illinois, coterminous with the now defunct Belleville Township. The population was 44,478 according to the Census Bureau's 2010 data, making it the largest city in southern Illinois.
It is the eighth-most populated city in the state outside the Chicago metropolitan area, and the most-populated city in the state south of Springfield. It is the county seat of St. Clair County, and the seat of the Roman Catholic Diocese of Belleville and the National Shrine of Our Lady of the Snows.
Belleville is the most-populated city in the Metro-East region of the St. Louis Metropolitan Area and in Southern Illinois. 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.
George Blair named the city of Belleville in 1814. Because Blair donated an acre of his land for the town square and an additional 25 acres (10 ha) adjoining the square for the new county seat, the legislature transferred the county seat from the village of Cahokia.