Belleville (21,122), the county seat of St. Clair County, is located near the divide between the Mississippi and Kaskaskia rivers. It is an important coal-mining and manufacturing center. Scott Aviation Field, at which hundreds of aviators received their training during the world-war, is located at Belleville.
St. Clair County stands next to Cook County in population. Two-thirds of the people of the county live in the two cities of East St. Louis and Belleville. Smaller cities of the county contain more than 10 per cent of the population of the county. The western portions of Madison and St. Clair counties from Alton to Belleville, a distance of 30 miles, form an urban district of the St. Louis region, much as the cities of north eastern Illinois form an urban district in the Chicago region.
Columbia (2,076), and Waterloo (2,091), the county scat, are the principal towns of Monroe County.
Cities of the Kaskaskia Basin.—The Kaskaskia River Basin is nearly 200 miles in length with an average width of about 30 miles. It lies in a northeast-southwest direction, extending from Champaign County to Randolph County, approaching within 40 miles of the Indiana state line. It has an area of 5,710 square miles, or one-tenth of the area of the state. Champaign and Urbana are on the divide between the Kas kaskia and Wabash basins and will be included with the cities of the Wabash Basin.
Sullivan (2,621) is the county seat of Moultrie County, and Shelbyville (3,590) of Shelby County.
Pana (6,055), in the southeast corner of Christian County, is an important coal-mining center.
In Montgomery County are found Nokomis (1,872), Witt (2,170), Hillsboro (3,424), the county seat, and Litchfield (5,971). Coal-mining is important at these cities.
Mount Olive (3,501) is in the southeast corner of Macoupin County on the western margin of the Kaskaskia Basin. It lies in the rich coal district, and is only a few miles from Gillespie, . Benld, and Staunton.
Vandalia (2,974), the county seat of Fayette County, was the state capital for twenty years, 1S19 to 1S39. The old capitol is now the county courthouse.
Greenville (3,178) is the county seat of Bond County. Carlyle (1,982) is the county seat of Clinton County.
Breese (2,128) is in the same county.
In that portion of St. Clair County included in the Kaskaskia Basin are O'Fallon (2,018), Lebanon (1,907), Mascoutah (2,081), Millstadt (1,140), New Athens (1,131), and Marissa (2,004).
Salem (2,669) is the county seat of Marion County. Near Odin (1,400) is found one of the state agricultural experiment fields.
Centralia (9,680), at the western margin of Marion County, is a coal-mining center. It is the most important railroad center and the largest city located within the borders of the Kaskaskia Basin. Belleville and Champaign, on the edges of the basin, are larger than Centralia.
Nashville (2,135) is the county seat of Washington County. Sparta (3,081) is the largest city in Randolph County.
Chester (2,747), the county seat of Randolph County, is the seat of the Southern Illinois State Penitentiary and of a state hospital. Chester is located on the Mississippi about 10 miles below the present junction of the Kaskaskia with the Mississippi. Before the cut-off was made forming Kaskaskia Island, the Kaskaskia River joined the Mississippi just above Chester. The Mississippi at present occupies, for a distance of about 10 miles, the former lower course of the Kaskaskia.
Kaskaskia (142), or New Kaskaskia, as it is called to dis tinguish it from the noted settlement of colonial days, is a village located on Kaskaskia Island. It is an Illinois village located west of the Mississippi River.
Cities of the Big Muddy Basin.—The Big Muddy River Basin has an area of 2,230 square miles, or 4 per cent of the area of the state. It contains ten cities having populations of 2,500 or more, and numerous smaller cities and villages. No other part of the state except the urban districts of Chicago and St. Louis has so many cities of more than 2,500 inhabitants in so small an area. None of these ten cities had a population of 10,000 in 1910. The basin contains the most productive coal district of the state, Williamson and Franklin counties alone producing about one-fourth of the output of the state. Coal mines are found near each of the ten cities except Mount Vernon.