St. Clair County is located in the southwestern region of Illinois. It is the sixth most populous county in the state, with a population of 270,056 as of the 2019 census. The county seat is Belleville, and the largest city is East St. Louis.

The county was established. The county is part of the Metro-East region of the St. Louis, MO-IL Metropolitan Statistical Area.

The county government is composed of a board of commissioners, which is the legislative body, and an executive branch headed by the County Executive. The county is divided into 24 townships, which provide local services.

The county is served by two major highways, Interstate 64 and Interstate 55, as well as several state highways. The county is also served by two airports, MidAmerica St. Louis Airport and Scott Air Force Base.

The county is home to several higher education institutions, including Southern Illinois University Edwardsville, Southwestern Illinois College, and McKendree University.

The county is home to several parks and recreational areas, including the Cahokia Mounds State Historic Site, the St. Clair County State Fish and Wildlife Area, and the Carlyle Lake State Recreation Area.

For the most up-to-date and in-depth information, please check the public records links below.