33 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Celina | 1 | 10,949 | 10,933 | 0.04% | 2,178 | 5 | City |
| Celina | 2 | 10,949 | 10,929 | 0.04% | 2,178 | 5 | City |
| Coldwater | 3 | 4,719 | 4,772 | -0.21% | 2,434 | 2 | Village |
| Coldwater | 4 | 4,719 | 4,769 | -0.21% | 2,434 | 2 | Village |
| St. Henry | 5 | 2,609 | 2,601 | 0.04% | 1,512 | 2 | Village |
| St. Henry | 6 | 2,609 | 2,602 | 0.04% | 1,512 | 2 | Village |
| Gibson | 7 | 2,169 | 2,125 | 0.98% | 96 | 23 | Township |
| Gibson | 8 | 2,169 | 2,123 | 0.98% | 96 | 23 | Township |
| Recovery | 9 | 1,482 | 1,512 | 0% | 61 | 24 | Township |
| Recovery | 10 | 1,482 | 1,511 | 0% | 61 | 24 | Township |
| Fort Recovery | 11 | 1,468 | 1,498 | -0.41% | 1,190 | 1 | Village |
| Fort Recovery | 12 | 1,468 | 1,497 | -0.41% | 1,190 | 1 | Village |
| Maria Stein | 13 | 1,390 | 1,141 | 7.17% | 274 | 5 | CDP |
| Union | 14 | 1,346 | 1,355 | 0.22% | 37 | 36 | Township |
| Union | 15 | 1,346 | 1,355 | 0.22% | 37 | 36 | Township |
| Washington | 16 | 1,275 | 1,221 | 1.35% | 35 | 36 | Township |
| Washington | 17 | 1,275 | 1,223 | 1.35% | 35 | 36 | Township |
| Center | 18 | 1,081 | 1,100 | 0% | 36 | 30 | Township |
| Center | 19 | 1,081 | 1,099 | 0% | 36 | 30 | Township |
| Rockford | 20 | 1,027 | 1,046 | -0.39% | 1,189 | 1 | Village |
| Rockford | 21 | 1,027 | 1,045 | -0.39% | 1,189 | 1 | Village |
| Liberty | 22 | 924 | 913 | 0.54% | 26 | 36 | Township |
| Liberty | 23 | 924 | 913 | 0.54% | 26 | 36 | Township |
| Black Creek | 24 | 649 | 622 | 1.72% | 18 | 36 | Township |
| Black Creek | 25 | 649 | 622 | 1.72% | 18 | 36 | Township |
| Mendon | 26 | 609 | 628 | -0.65% | 1,117 | 1 | Village |
| Mendon | 27 | 609 | 628 | -0.65% | 1,117 | 1 | Village |
| Chickasaw | 28 | 353 | 358 | -0.28% | 1,471 | 0 | Village |
| Chickasaw | 29 | 353 | 358 | -0.28% | 1,471 | 0 | Village |
| Burkettsville | 30 | 265 | 272 | -0.75% | 1,532 | 0 | Village |
| Burkettsville | 31 | 265 | 272 | -0.75% | 1,532 | 0 | Village |
| Montezuma | 32 | 148 | 153 | -0.67% | 1,451 | 0 | Village |
| Montezuma | 33 | 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 33 cities in Mercer County, Ohio.