16 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Celina | 1 | 10,949 | 10,929 | 0.04% | 2,178 | 5 | City |
| Coldwater | 2 | 4,719 | 4,769 | -0.21% | 2,434 | 2 | Village |
| St. Henry | 3 | 2,609 | 2,602 | 0.04% | 1,512 | 2 | Village |
| Gibson | 4 | 2,169 | 2,123 | 0.98% | 96 | 23 | Township |
| Recovery | 5 | 1,482 | 1,511 | 0% | 61 | 24 | Township |
| Fort Recovery | 6 | 1,468 | 1,497 | -0.41% | 1,190 | 1 | Village |
| Union | 7 | 1,346 | 1,355 | 0.22% | 37 | 36 | Township |
| Washington | 8 | 1,275 | 1,223 | 1.35% | 35 | 36 | Township |
| Center | 9 | 1,081 | 1,099 | 0% | 36 | 30 | Township |
| Rockford | 10 | 1,027 | 1,045 | -0.39% | 1,189 | 1 | Village |
| Liberty | 11 | 924 | 913 | 0.54% | 26 | 36 | Township |
| Black Creek | 12 | 649 | 622 | 1.72% | 18 | 36 | Township |
| Mendon | 13 | 609 | 628 | -0.65% | 1,117 | 1 | Village |
| Chickasaw | 14 | 353 | 358 | -0.28% | 1,471 | 0 | Village |
| Burkettsville | 15 | 265 | 272 | -0.75% | 1,532 | 0 | Village |
| Montezuma | 16 | 148 | 153 | -0.67% | 1,451 | 0 | Village |
Celina is the largest city in Mercer County, with a population of 10,949.
Montezuma is the smallest city in Mercer County, with a population of 148.
There are 16 cities in Mercer County, Ohio.