St. Clair County, Illinois in the context of "Illinois counties"

Greater St. Louis is the 23rd-largest metropolitan statistical area (MSA) in the United States consisting with an MSA population more than 2.8 million, and almost 3 million CSA the largest in Missouri, and the second-largest in Illinois. Its core city—St. Louis, Missouri—sits in the geographic center of the metro area, on the west bank of the Mississippi River. The river bisects the metro area geographically between Illinois and Missouri, although the latter portion is much more populous. The MSA includes St. Louis County, which is independent of the City of St. Louis; their two populations are generally tabulated separately.

The St. Louis, MO-IL metropolitan statistical area (MSA) includes the City of St. Louis; the Illinois counties of Bond, Calhoun, Clinton, Jersey, Macoupin, Madison, Monroe, and St. Clair (known collectively as the Metro East); and the Missouri counties of Crawford (only the City of Sullivan), Franklin, Jefferson, Lincoln, St. Charles, St. Louis (separate from and not inclusive of the city of St. Louis), and Warren.

Cahokia is a settlement and former village in St. Clair County, Illinois, United States, founded as a colonial French mission in 1689. Cahokia is on the east side of the Mississippi River in the Greater St. Louis metropolitan area. As of the 2010 census, it had a population of 15,241. On May 6, 2021, the village was incorporated into the new city of Cahokia Heights.

The name refers to one of the clans of the historic Illiniwek confederacy, who met early French explorers to the region. Early European settlers named the nearby (and long-abandoned) Cahokia Mounds in present-day Madison County after the Illini clan. The UNESCO World Heritage Site and State Historic Park were developed by the Mississippian culture, active here from 900 to 1500 AD. A connection to the clan is possible but unknown. The area was part of an extensive urban complex, the largest of the far-flung Mississippian culture territory through the Mississippi and Ohio River Valleys.

There are 72 counties in the US state of Wisconsin. The land that eventually became Wisconsin was transferred from British to American control with the 1783 signing of the Treaty of Paris. It was an unorganized part of the Northwest Territory until 1802 when all of the land from St. Louis north to the Canadian border was organized as St. Clair County. When Illinois was admitted to the union in 1818, Wisconsin became part of the Territory of Michigan and divided into two counties: Brown County in the northeast along Lake Michigan and Crawford County in the southwest along the Mississippi River. Iowa County was formed in 1829 from the Crawford County land south of the Wisconsin River. Brown County's southern portion was used to form Milwaukee County in 1834. The state of Wisconsin was created from Wisconsin Territory on May 29, 1848, with 28 counties.

The most populous county in the state is Milwaukee County at 924,740 people at the 2024 Census estimate. The county with the least population is Menominee County with 4,286 residents; the Menominee Indian Reservation is co-extensive with the county. Pepin County is the smallest in area, with 231.98 square miles (600.8 km); Marathon is the largest, having 1,544.91 square miles (4,001.3 km).

Collinsville is a city located mainly in Madison County and partially in St. Clair County, Illinois, United States. As of the 2020 census, the city had a population of 24,366. Collinsville is approximately 14 miles (23 km) east of St. Louis, Missouri, and is part of that city's Metro East area.

Collinsville is the location of Cahokia Mounds State Historic Site, a National Historic Landmark and UNESCO World Heritage Site. This prehistoric urban complex is estimated to have had a population of thousands at its peak, long before European exploration in the area. The city is also known for the Brooks Catsup Bottle Water Tower, the world's largest ketchup bottle, and is billed as the world's horseradish capital.

Belleville is a city in St. Clair County, Illinois, United States, and its county seat. It is a southeastern suburb of St. Louis. The population was 42,404 at the 2020 census, making it the most populated city in the Metro East region of Greater St. Louis, and in all of Southern Illinois south of Springfield. Due to its proximity to Scott Air Force Base, the city has a significant population of military and federal civilian personnel. It is the seat of the Roman Catholic Diocese of Belleville and home to the National Shrine of Our Lady of the Snows.

Scott Air Force Base (IATA: BLV, ICAO: KBLV, FAA LID: BLV) is a United States Air Force base in St. Clair County, Illinois, near Belleville and O'Fallon, 17 miles (27 km) east-southeast of downtown St. Louis. Originally Scott Field, it was one of 32 Air Service training camps established after the United States entered World War I in April 1917. The present base serves as the headquarters of Air Mobility Command (AMC) and its showcase wing, and it is also the headquarters of the U.S. Transportation Command, a Unified Combatant Command that coordinates transportation across all the services.

The base is operated by the 375th Air Mobility Wing (375 AMW) and is also home to the Air Force Reserve Command's 932d Airlift Wing (932 AW) and the Illinois Air National Guard's 126th Air Refueling Wing (126 ARW), the latter two units being operationally under AMC.