Founded in 1790, St. Clair County is one of 102 counties in the state of Illinois. The city of Belleville is the county seat. With FIPS code of 163, St. Clair County has a population of 254,796 and area of 657 square miles (1,702 km2).
List of all cities in Saint Clair County, IL alphabetically
| City/Town | Postal Code | Area Code |
| Alorton, IL | 62207 | 618/730 |
| Belleville, IL | 62220 | 618/730 |
| 62221 | 618/730 | |
| 62222 | 618/730 | |
| 62223 | 618/730 | |
| 62225 | 618/730 | |
| 62226 | 618/730 | |
| 62269 | 618/730 | |
| Brooklyn, IL | 62059 | 618/730 |
| Cahokia, IL | 62206 | 618/730 |
| Caseyville, IL | 62232 | 618/730 |
| 62203 | 618/730 | |
| 62205 | 618/730 | |
| 62207 | 618/730 | |
| Darmstadt, IL | 62255 | 618/730 |
| Dupo, IL | 62239 | 618/730 |
| East Carondelet, IL | 62240 | 618/730 |
| East Saint Louis, IL | 62201 | 618/730 |
| 62202 | 618/730 | |
| 62203 | 618/730 | |
| 62204 | 618/730 | |
| 62205 | 618/730 | |
| 62206 | 618/730 | |
| 62207 | 618/730 | |
| 62208 | 618/730 | |
| Fairmont City, IL | 62201 | 618/730 |
| Fairview Heights, IL | 62208 | 618/730 |
| 62232 | 618/730 | |
| Fayetteville, IL | 62258 | 618/730 |
| Freeburg, IL | 62243 | 618/730 |
| Hollywood Heights, IL | 62232 | 618/730 |
| IMBS, IL | 62240 | 618/730 |
| Lebanon, IL | 62254 | 618/730 |
| Lenzburg, IL | 62255 | 618/730 |
| Lovejoy, IL | 62059 | 618/730 |
| Marissa, IL | 62257 | 618/730 |
| Marrisa, IL | 62257 | 618/730 |
| Mascoutah, IL | 62258 | 618/730 |
| Millstadt, IL | 62260 | 618/730 |
| National Stock Yard, IL | 62071 | 618/730 |
| 62071 | 618/730 | |
| New Athens, IL | 62264 | 618/730 |
| O Fallon, IL | 62269 | 618/730 |
| Rentchler, IL | 62221 | 618/730 |
| Saint Libory, IL | 62282 | 618/730 |
| Sauget, IL | 62201 | 618/730 |
| Sauget, IL | 62206 | 618/730 |
| Scott Air Force Base, IL | 62225 | 618/730 |
| Shiloh, IL | 62221 | 618/730 |
| 62269 | 618/730 | |
| Signal Hill, IL | 62223 | 618/730 |
| Smithton, IL | 62285 | 618/730 |
| Stites, IL | 62059 | 618/730 |
| Summerfield, IL | 62289 | 618/730 |
| Swansea, IL | 62220 | 618/730 |
| 62221 | 618/730 | |
| 62223 | 618/730 | |
| 62226 | 618/730 | |
| Washington Park, IL | 62204 | 618/730 |
| 62205 | 618/730 |