18 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Monmouth | 1 | 9,659 | 9,947 | 0.32% | 262 | 37 | Township |
| Monmouth | 2 | 8,569 | 8,916 | -0.81% | 2,020 | 4 | City |
| Roseville | 3 | 1,105 | 1,162 | -0.63% | 30 | 37 | Township |
| Tompkins | 4 | 848 | 893 | -0.59% | 23 | 37 | Township |
| Roseville | 5 | 829 | 878 | -1.19% | 1,122 | 1 | Village |
| Kirkwood | 6 | 640 | 677 | -1.23% | 682 | 1 | Village |
| Greenbush | 7 | 511 | 537 | -0.58% | 14 | 36 | Township |
| Coldbrook | 8 | 418 | 437 | -0.48% | 12 | 36 | Township |
| Cameron | 9 | 414 | 146 | 7.25% | 654 | 1 | CDP |
| Floyd | 10 | 396 | 414 | -0.5% | 11 | 36 | Township |
| Kelly | 11 | 351 | 369 | -0.57% | 10 | 35 | Township |
| Hale | 12 | 319 | 335 | -0.31% | 9 | 37 | Township |
| Ellison | 13 | 298 | 315 | -0.67% | 8 | 36 | Township |
| Berwick | 14 | 295 | 308 | -0.34% | 8 | 36 | Township |
| Little York | 15 | 264 | 281 | -1.49% | 1,184 | 0 | Village |
| Lenox | 16 | 253 | 270 | -1.56% | 7 | 36 | Township |
| Swan | 17 | 229 | 241 | -0.87% | 6 | 35 | Township |
| Point Pleasant | 18 | 132 | 137 | 0% | 4 | 36 | Township |
Monmouth is the largest city in Warren County, with a population of 9,659.
Point Pleasant is the smallest city in Warren County, with a population of 132.
There are 18 cities in Warren County, Illinois.