List of all settlements:
- Algonac, St. Clair
- Alorton, St. Clair
- Appleton City, St. Clair
- Argo, St. Clair
- Ashville, St. Clair
- Belleville, St. Clair
- Brooklyn, St. Clair
- Cahokia, St. Clair
- Capac, St. Clair
- Caseyville, St. Clair
- Centreville, St. Clair
- Collins, St. Clair
- Collinsville, St. Clair
- Columbia, St. Clair
- Dupo, St. Clair
- East Carondelet, St. Clair
- East St. Louis, St. Clair
- Emmett, St. Clair
- Fairmont City, St. Clair
- Fairview Heights, St. Clair
- Fayetteville, St. Clair
- Freeburg, St. Clair
- Hecker, St. Clair
- Lebanon, St. Clair
- Leeds, St. Clair
- Lenzburg, St. Clair
- Lowry City, St. Clair
- Madison, St. Clair
- Margaret, St. Clair
- Marine City, St. Clair
- Marissa, St. Clair
- Marysville, St. Clair
- Mascoutah, St. Clair
- Memphis, St. Clair
- Millstadt, St. Clair
- Moody, St. Clair
- New Athens, St. Clair
- New Baden, St. Clair
- O'Fallon, St. Clair
- Odenville, St. Clair
- Osceola, St. Clair
- Pearl Beach, St. Clair
- Pell City, St. Clair
- Port Huron, St. Clair
- Ragland, St. Clair
- Richmond, St. Clair
- Riverside, St. Clair
- Roscoe, St. Clair
- Sauget, St. Clair
- Scott AFB, St. Clair
- Shiloh, St. Clair
- Smithton, St. Clair
- Springville, St. Clair
- St. Libory, St. Clair
- Steele, St. Clair
- Summerfield, St. Clair
- Swansea, St. Clair
- Trussville, St. Clair
- Vincent, St. Clair
- Washington Park, St. Clair
- Yale, St. Clair