| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Watseka | 1 | 4,473 | 4,673 | -0.82% | 1,519 | 3 | City |
| Gilman | 2 | 1,666 | 1,746 | -0.89% | 508 | 3 | City |
| Onarga | 3 | 1,295 | 1,346 | -0.77% | 774 | 2 | Village |
| Clifton | 4 | 1,287 | 1,347 | -0.85% | 1,384 | 1 | Village |
| Milford | 5 | 1,106 | 1,158 | -0.9% | 1,648 | 1 | Village |
| Chebanse | 6 | 1,005 | 1,050 | -0.89% | 1,274 | 1 | Village |
| Sheldon | 7 | 923 | 966 | -0.86% | 1,226 | 1 | Village |
| Cissna Park | 8 | 773 | 810 | -0.9% | 1,066 | 1 | Village |
| Ashkum | 9 | 712 | 743 | -0.84% | 853 | 1 | Village |
| Danforth | 10 | 564 | 589 | -0.88% | 1,180 | 0 | Village |
| Crescent City | 11 | 524 | 551 | -0.95% | 1,149 | 0 | Village |
| Sun River Terrace | 12 | 478 | 495 | -0.62% | 823 | 1 | Village |
| Buckley | 13 | 457 | 480 | -1.08% | 1,446 | 0 | Village |
| Loda | 14 | 326 | 342 | -0.91% | 222 | 1 | Village |
| Martinton | 15 | 314 | 330 | -0.95% | 1,146 | 0 | Village |
| Beaverville | 16 | 292 | 305 | -1.02% | 1,062 | 0 | Village |
| Donovan | 17 | 236 | 249 | -1.26% | 720 | 0 | Village |
| Woodland | 18 | 235 | 245 | -0.84% | 480 | 0 | Village |
| Thawville | 19 | 205 | 215 | -0.97% | 668 | 0 | Village |
| Wellington | 20 | 195 | 205 | -1.02% | 819 | 0 | Village |
| Papineau | 21 | 131 | 136 | -0.76% | 630 | 0 | Village |
| Iroquois | 22 | 130 | 133 | -0.76% | 229 | 1 | Village |
Watseka is the largest city in Iroquois County, with a population of 4,473.
Iroquois is the smallest city in Iroquois County, with a population of 130.
There are 22 cities in Iroquois County, Illinois.