| Capital: | Belleville |
|---|---|
| Origen y Formación del condado: | original two counties |
| Población: | 270,056 habitantes |
| Área: | 664 sq mi |
| Localización del condado dentro de Illinois: |
|
Localidades en St. Clair, Illinois
- Alorton
- Belleville
- Brooklyn
- Cahokia
- Canteen Township St. Clair County
- Caseyville
- Caseyville Township St. Clair County
- Centreville
- Centreville Township St. Clair County
- Collinsville
- Columbia
- Darmstadt
- Dupo
- East Carondelet
- East St. Louis
- Engelmann Township St. Clair County
- Fairmont City
- Fairview Heights
- Fayetteville
- Fayetteville Township St. Clair County
- Floraville
- Freeburg
- Freeburg Township St. Clair County
- Hecker
- Lebanon
- Lebanon Township St. Clair County
- Lenzburg
- Lenzburg Township St. Clair County
- Madison
- Marissa
- Marissa Township St. Clair County
- Mascoutah
- Mascoutah Township St. Clair County
- Millstadt
- Millstadt Township St. Clair County
- National Stock Yards
- New Athens
- New Athens Township St. Clair County
- New Baden
- O'Fallon
- O Fallon Township St. Clair County
- Ofallon Township St Clair County
- Paderborn
- Prairie Du Long Township St. Clair County
- Rentchler
- Sauget
- Scott Afb
- Scott Air Force Base
- Shiloh
- Shiloh Valley Township St. Clair County
- Smithton
- Smithton Township St. Clair County
- St. Clair Township St. Clair County
- St. Libory
- Stites Township St. Clair County
- Stookey Township St. Clair County
- Sugarloaf Township St. Clair County
- Summerfield
- Swansea
- Washington Park