17 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Monmouth | 1 | 9,690 | 9,947 | 0.32% | 263 | 37 | Township |
| Monmouth | 2 | 8,500 | 8,916 | -0.81% | 2,004 | 4 | City |
| Roseville | 3 | 1,098 | 1,162 | -0.63% | 30 | 37 | Township |
| Tompkins | 4 | 843 | 893 | -0.59% | 23 | 37 | Township |
| Roseville | 5 | 819 | 878 | -1.21% | 1,108 | 1 | Village |
| Kirkwood | 6 | 633 | 677 | -1.09% | 674 | 1 | Village |
| Greenbush | 7 | 508 | 537 | -0.59% | 14 | 36 | Township |
| Coldbrook | 8 | 416 | 437 | -0.48% | 12 | 36 | Township |
| Floyd | 9 | 394 | 414 | -0.51% | 11 | 36 | Township |
| Kelly | 10 | 349 | 369 | -0.57% | 10 | 35 | Township |
| Hale | 11 | 318 | 335 | -0.31% | 9 | 37 | Township |
| Ellison | 12 | 296 | 315 | -0.67% | 8 | 36 | Township |
| Berwick | 13 | 294 | 308 | -0.34% | 8 | 36 | Township |
| Little York | 14 | 261 | 281 | -1.14% | 1,170 | 0 | Village |
| Lenox | 15 | 249 | 270 | -1.58% | 7 | 36 | Township |
| Swan | 16 | 227 | 241 | -0.87% | 6 | 35 | Township |
| Point Pleasant | 17 | 132 | 137 | 0% | 4 | 36 | Township |
Monmouth is the largest city in Warren County, with a population of 9,690.
Point Pleasant is the smallest city in Warren County, with a population of 132.
There are 17 cities in Warren County, Illinois.