Belleville (French: Belle ville, meaning "Beautiful city") is a city in St. Clair County, Illinois, United States, co-extensive with Belleville Township. As of the 2010 census, the city has a population of 44,478. It is the eighth-most populated city outside of the Chicago Metropolitan Area and the most populated city south of Springfield in the state of Illinois. 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.

The city of Belleville was named by George Blair in 1814. Blair was born in 1760 and his father was born in Scotland. Blair donated an acre of his land for the Town Square and an additional 25 acres (100,000 m²) that adjoined the Square for the new County Seat, causing the county seat to be transferred from the village of Cahokia. Belleville was incorporated as a village in 1819, and became a city in 1850. It is said that Blair named the city Belleville (French for beautiful city) because he believed that a French name would attract new residents. Since major immigration in the mid-19th century occurred following revolutions in Germany, most of the population is of German heritage.

Illinois (ⁱ/ˌɪlɨˈnɔɪ/ IL-i-NOY) is the 25th most extensive and the 5th most populous of the 50 United States, and is often noted as a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal, timber, and petroleum in the south, Illinois has a broad economic base. Illinois is a major transportation hub. The Port of Chicago connects the state to other global ports from the Great Lakes, via the Saint Lawrence Seaway, to the Atlantic Ocean; as well as the Great Lakes to the Mississippi River, via the Illinois River. For decades, O'Hare International Airport has ranked as one of the world's busiest airports. Illinois has long had a reputation as a bellwether both in social and cultural terms and politics.

Although the state's largest population centers today are in northern Illinois, originally the state's population grew from south to north, with settlers arriving from Kentucky in the 1810s. In 1818, Illinois achieved statehood. Chicago was founded in the 1830s on the banks of the Chicago River, one of the few natural harbors on southern Lake Michigan. Railroads and John Deere's invention of the self-scouring steel plow turned Illinois' rich prairie into some of the world's most productive and valuable farmlands, attracting immigrant farmers from Germany and Sweden. By 1900, the growth of industrial jobs in the northern cities and coal mining in the central and southern areas attracted immigrants from Eastern and Southern Europe. Illinois was an important manufacturing center during both world wars. The Great Migration established a large community of African Americans in Chicago that created the city's famous jazz and blues cultures.