| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Monticello | 1 | 6,095 | 5,947 | 0.25% | 1,572 | 4 | City |
| Bement | 2 | 1,454 | 1,481 | -0.55% | 1,869 | 1 | Village |
| Cerro Gordo | 3 | 1,307 | 1,324 | -0.38% | 1,793 | 1 | Village |
| Mansfield | 4 | 917 | 932 | -0.43% | 1,805 | 1 | Village |
| Hammond | 5 | 497 | 505 | -0.4% | 657 | 1 | Village |
| De Land | 6 | 444 | 453 | -0.67% | 1,047 | 0 | Village |
| Cisco | 7 | 252 | 258 | -0.79% | 1,385 | 0 | Village |
Monticello is the largest city in Piatt County, with a population of 6,095.
Cisco is the smallest city in Piatt County, with a population of 252.
There are 7 cities in Piatt County, Illinois.