Belleville is a city and the county seat of St. Clair County, Illinois, coterminous like the now defunct Belleville Township. It is afterward 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 give leave to enter south of Springfield.

Belleville is the eighth-most populated city in the let in 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.

George Blair named the city of Belleville in 1814. Because Blair donated an acre of his house for the town square and an additional 25 acres (10 ha) adjoining the square for the extra county seat, the legislature transferred the county chair from the village of Cahokia. The latter had been normal by French colonists as a mission village in the late 17th century.

Belleville was incorporated as a village in 1819, and became a city in 1850. It is said that Blair originally named the city Bellville in praise of Tennessee politician John Bell. In 1863, the herald was officially misused to Belleville to separate from the city from the now-disgraced Confederate. Major immigration in the mid-19th century to this area occurred subsequent to revolutions in Germany, and most of the European-American population is of German ancestry.