19 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Harter township | 1 | 5,965 | 6,133 | -0.48% | 107 | 55.84 | Township |
| Flora | 2 | 4,654 | 4,796 | -0.6% | 992 | 4.69 | City |
| Flora township | 3 | 3,022 | 2,983 | 0.5% | 83 | 36.48 | Township |
| Louisville township | 4 | 1,644 | 1,704 | -0.66% | 45 | 36.41 | Township |
| Louisville | 5 | 1,102 | 1,144 | -0.72% | 1,331 | 0.83 | Village |
| Clay City township | 6 | 1,090 | 1,133 | -0.64% | 27 | 40.23 | Township |
| Clay City | 7 | 817 | 854 | -0.85% | 458 | 1.78 | Village |
| Xenia township | 8 | 623 | 649 | -0.8% | 33 | 18.63 | Township |
| Blair township | 9 | 596 | 618 | -0.5% | 16 | 36.20 | Township |
| Larkinsburg township | 10 | 563 | 578 | -0.53% | 15 | 37.13 | Township |
| Pixley township | 11 | 525 | 543 | -0.76% | 12 | 45.07 | Township |
| Xenia | 12 | 366 | 381 | -0.81% | 742 | 0.49 | Village |
| Songer township | 13 | 334 | 348 | -0.89% | 9 | 37.38 | Township |
| Oskaloosa township | 14 | 328 | 342 | -0.91% | 9 | 37.40 | Township |
| Hoosier township | 15 | 306 | 318 | -0.65% | 9 | 35.63 | Township |
| Bible Grove township | 16 | 285 | 303 | -1.38% | 8 | 35.48 | Township |
| La Clede | 17 | 215 | 33 | 6.97% | 700 | 0.31 | CDP |
| Iola | 18 | 95 | 99 | -1.04% | 99 | 0.96 | Village |
| Sailor Springs | 19 | 87 | 91 | -1.14% | 335 | 0.26 | Village |
Harter township is the largest city in Clay County, with a population of 5,965.
Sailor Springs is the smallest city in Clay County.
There are 19 cities in Clay County, Illinois.