Belleville is a city and the county seat of St. Clair County, Illinois, United States.[3] It is located within Greater St. Louis. The population was 42,404 at the 2020 census, making it the most-populated city in Southern Illinois and in the Metro East region of Greater St. Louis.
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.[citation needed] It is also the seat of the Roman Catholic Diocese of Belleville and the National Shrine of Our Lady of the Snows.
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.
The latter had been established by French colonists as a mission village in the late 17th century.
