17 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Celina | 1 | 10,855 | 10,930 | -0.14% | 2,159 | 5.03 | City |
| Coldwater | 2 | 4,673 | 4,770 | -0.4% | 2,410 | 1.94 | Village |
| St. Henry | 3 | 2,601 | 2,603 | 0% | 1,508 | 1.73 | Village |
| Gibson township | 4 | 2,145 | 2,124 | 0.42% | 95 | 22.54 | Township |
| Recovery township | 5 | 1,465 | 1,513 | -0.61% | 60 | 24.29 | Township |
| Fort Recovery | 6 | 1,460 | 1,500 | -0.54% | 1,183 | 1.23 | Village |
| Maria Stein | 7 | 1,390 | 1,141 | 7.17% | 274 | 5.08 | CDP |
| Union township | 8 | 1,334 | 1,356 | -0.15% | 37 | 36.38 | Township |
| Washington township | 9 | 1,265 | 1,223 | 0.96% | 35 | 36.34 | Township |
| Center township | 10 | 1,077 | 1,100 | -0.19% | 36 | 30.18 | Township |
| Rockford | 11 | 1,019 | 1,044 | -0.49% | 1,179 | 0.86 | Village |
| Liberty township | 12 | 913 | 913 | 0.11% | 25 | 35.90 | Township |
| Black Creek township | 13 | 628 | 623 | 0% | 18 | 35.78 | Township |
| Mendon | 14 | 601 | 628 | -0.83% | 1,103 | 0.55 | Village |
| Chickasaw | 15 | 346 | 356 | -0.57% | 1,442 | 0.24 | Village |
| Burkettsville | 16 | 261 | 270 | -0.76% | 1,509 | 0.17 | Village |
| Montezuma | 17 | 148 | 153 | -0.67% | 1,451 | 0.10 | Village |
Celina is the largest city in Mercer County, with a population of 10,855.
Montezuma is the smallest city in Mercer County.
There are 17 cities in Mercer County, Ohio.