8 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Monticello | 1 | 6,063 | 5,950 | 0.38% | 1,563 | 3.88 | City |
| Bement | 2 | 1,457 | 1,484 | -0.34% | 1,873 | 0.78 | Village |
| Cerro Gordo | 3 | 1,300 | 1,315 | -0.23% | 1,783 | 0.73 | Village |
| Mansfield | 4 | 922 | 936 | -0.32% | 1,815 | 0.51 | Village |
| Hammond | 5 | 497 | 506 | -0.4% | 657 | 0.76 | Village |
| De Land | 6 | 441 | 450 | -0.45% | 1,040 | 0.42 | Village |
| Cisco | 7 | 251 | 255 | -0.4% | 1,379 | 0.18 | Village |
| White Heath | 8 | 141 | 153 | -6.62% | 413 | 0.34 | CDP |
Monticello is the largest city in Piatt County, with a population of 6,063.
White Heath is the smallest city in Piatt County.
There are 8 cities in Piatt County, Illinois.