7 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Monticello | 1 | 6,041 | 5,948 | 0.27% | 1,558 | 4 | City |
| Bement | 2 | 1,437 | 1,482 | -0.48% | 1,847 | 1 | Village |
| Cerro Gordo | 3 | 1,284 | 1,317 | -0.39% | 1,761 | 1 | Village |
| Mansfield | 4 | 910 | 934 | -0.44% | 1,791 | 1 | Village |
| Hammond | 5 | 494 | 506 | -0.4% | 653 | 1 | Village |
| De Land | 6 | 438 | 450 | -0.45% | 1,033 | 0 | Village |
| Cisco | 7 | 249 | 258 | -0.4% | 1,368 | 0 | Village |
Monticello is the largest city in Piatt County, with a population of 6,041.
Cisco is the smallest city in Piatt County, with a population of 249.
There are 7 cities in Piatt County, Illinois.