19 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Marshall | 1 | 4,372 | 4,558 | -0.95% | 138 | 32 | Township |
| Marshall | 2 | 3,822 | 3,951 | -0.55% | 1,042 | 4 | City |
| Casey | 3 | 3,344 | 3,487 | -0.92% | 92 | 36 | Township |
| Casey | 4 | 2,348 | 2,432 | -0.59% | 895 | 3 | City |
| Wabash | 5 | 2,010 | 2,103 | -0.94% | 28 | 73 | Township |
| Martinsville | 6 | 1,462 | 1,527 | -0.88% | 35 | 42 | Township |
| Martinsville | 7 | 1,068 | 1,113 | -0.65% | 528 | 2 | City |
| Westfield | 8 | 809 | 843 | -0.74% | 23 | 35 | Township |
| Westfield | 9 | 621 | 649 | -0.8% | 35 | 18 | Township |
| Westfield | 10 | 512 | 535 | -0.78% | 524 | 1 | Village |
| York | 11 | 478 | 498 | -0.83% | 15 | 31 | Township |
| Anderson | 12 | 413 | 430 | -0.72% | 13 | 32 | Township |
| Johnson | 13 | 353 | 373 | -1.4% | 10 | 36 | Township |
| Dolson | 14 | 341 | 360 | -1.45% | 10 | 35 | Township |
| Melrose | 15 | 326 | 339 | -0.91% | 10 | 33 | Township |
| Darwin | 16 | 319 | 334 | -0.93% | 12 | 27 | Township |
| Orange | 17 | 253 | 262 | -0.78% | 7 | 37 | Township |
| Parker | 18 | 156 | 164 | -1.27% | 4 | 36 | Township |
| Douglas | 19 | 119 | 130 | -2.46% | 7 | 18 | Township |
Marshall is the largest city in Clark County, with a population of 4,372.
Douglas is the smallest city in Clark County, with a population of 119.
There are 19 cities in Clark County, Illinois.