| Locality | Post Code |
|---|---|
| Saint Libory, Saint Clair | 62282 |
| Sauget, Saint Clair | 62206 |
| Scott Air Force Base, Saint Clair | 62225 |
| Shiloh, Saint Clair | 62269 |
| Signal Hill, Saint Clair | 62223 |
| Smithton, Saint Clair | 62285 |
| Stites, Saint Clair | 62059 |
| Summerfield, Saint Clair | 62289 |
| Swansea, Saint Clair | 62226 |
| Washington Park, Saint Clair | 62204, 62205 |