22 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Watseka | 1 | 4,408 | 4,669 | -0.97% | 1,497 | 3 | City |
| Gilman | 2 | 1,640 | 1,741 | -1.03% | 500 | 3 | City |
| Onarga | 3 | 1,271 | 1,340 | -0.86% | 759 | 2 | Village |
| Clifton | 4 | 1,269 | 1,347 | -1.01% | 1,365 | 1 | Village |
| Milford | 5 | 1,087 | 1,159 | -1.09% | 1,620 | 1 | Village |
| Chebanse | 6 | 992 | 1,049 | -0.9% | 1,257 | 1 | Village |
| Sheldon | 7 | 911 | 968 | -0.98% | 1,210 | 1 | Village |
| Cissna Park | 8 | 761 | 811 | -1.04% | 1,050 | 1 | Village |
| Ashkum | 9 | 702 | 743 | -0.99% | 841 | 1 | Village |
| Danforth | 10 | 559 | 592 | -0.89% | 1,169 | 0 | Village |
| Crescent City | 11 | 517 | 550 | -0.96% | 1,134 | 0 | Village |
| Buckley | 12 | 458 | 488 | -1.08% | 1,449 | 0 | Village |
| Sun River Terrace | 13 | 445 | 459 | -0.45% | 766 | 1 | Village |
| Loda | 14 | 324 | 345 | -0.92% | 221 | 1 | Village |
| Martinton | 15 | 314 | 335 | -0.95% | 1,146 | 0 | Village |
| Beaverville | 16 | 285 | 305 | -1.04% | 1,036 | 0 | Village |
| Donovan | 17 | 233 | 248 | -0.85% | 710 | 0 | Village |
| Woodland | 18 | 232 | 247 | -0.85% | 473 | 0 | Village |
| Thawville | 19 | 200 | 214 | -0.99% | 651 | 0 | Village |
| Wellington | 20 | 190 | 204 | -1.04% | 798 | 0 | Village |
| Iroquois | 21 | 129 | 134 | -0.77% | 228 | 1 | Village |
| Papineau | 22 | 127 | 135 | -0.78% | 611 | 0 | Village |
Watseka is the largest city in Iroquois County, with a population of 4,408.
Papineau is the smallest city in Iroquois County, with a population of 127.
There are 22 cities in Iroquois County, Illinois.