16 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Celina | 1 | 10,953 | 10,929 | 0.04% | 2,178 | 5 | City |
| Coldwater | 2 | 4,709 | 4,769 | -0.21% | 2,429 | 2 | Village |
| St. Henry | 3 | 2,611 | 2,602 | 0.08% | 1,514 | 2 | Village |
| Gibson | 4 | 2,190 | 2,123 | 0.97% | 97 | 23 | Township |
| Recovery | 5 | 1,482 | 1,511 | 0% | 61 | 24 | Township |
| Fort Recovery | 6 | 1,462 | 1,497 | -0.41% | 1,185 | 1 | Village |
| Union | 7 | 1,349 | 1,355 | 0.22% | 37 | 36 | Township |
| Washington | 8 | 1,292 | 1,223 | 1.33% | 36 | 36 | Township |
| Center | 9 | 1,081 | 1,099 | 0% | 36 | 30 | Township |
| Rockford | 10 | 1,024 | 1,045 | -0.29% | 1,185 | 1 | Village |
| Liberty | 11 | 929 | 913 | 0.54% | 26 | 36 | Township |
| Black Creek | 12 | 660 | 622 | 1.69% | 18 | 36 | Township |
| Mendon | 13 | 605 | 628 | -0.66% | 1,110 | 1 | Village |
| Chickasaw | 14 | 352 | 358 | -0.28% | 1,467 | 0 | Village |
| Burkettsville | 15 | 264 | 272 | -0.38% | 1,526 | 0 | Village |
| Montezuma | 16 | 147 | 153 | -0.68% | 1,441 | 0 | Village |
Celina is the largest city in Mercer County, with a population of 10,953.
Montezuma is the smallest city in Mercer County, with a population of 147.
There are 16 cities in Mercer County, Ohio.