Founded in 1819, Clark County is one of 102 counties in the state of Illinois. Historically, Clark County was formed from Crawford County. The city of Marshall is the county seat. With FIPS code of 23, Clark County has a population of 15,300 and area of 501 square miles (1,298 km2).
List of all cities in Clark County, IL alphabetically
| City/Town | Postal Code | Area Code |
| Albright, IL | 62441 | 217 |
| Casey, IL | 62420 | 217 |
| Clark Center, IL | 62441 | 217 |
| Clarksville, IL | 62441 | 217 |
| Cleone, IL | 62442 | 217 |
| Dennison, IL | 62423 | 217 |
| Marshall, IL | 62441 | 217 |
| Martinsville, IL | 62442 | 217 |
| Moonshine, IL | 62442 | 217 |
| Neadmore, IL | 62442 | 217 |
| Oliver, IL | 62441 | 217 |
| Parker, IL | 62474 | 217 |
| West Union, IL | 62477 | 217 |
| Westfield, IL | 62474 | 217 |