| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Celina | 1 | 10,930 | 10,933 | -0.05% | 2,174 | 5 | City |
| Coldwater | 2 | 4,699 | 4,764 | -0.36% | 2,423 | 2 | Village |
| St. Henry | 3 | 2,624 | 2,607 | 0% | 1,521 | 2 | Village |
| Fort Recovery | 4 | 1,470 | 1,498 | -0.41% | 1,191 | 1 | Village |
| Rockford | 5 | 1,033 | 1,053 | -0.58% | 1,196 | 1 | Village |
| Mendon | 6 | 608 | 630 | -0.82% | 1,116 | 1 | Village |
| Chickasaw | 7 | 350 | 356 | -0.28% | 1,458 | 0 | Village |
| Burkettsville | 8 | 264 | 271 | -0.75% | 1,526 | 0 | Village |
| Montezuma | 9 | 147 | 154 | -1.34% | 1,441 | 0 | Village |
Celina is the largest city in Mercer County, with a population of 10,930.
Montezuma is the smallest city in Mercer County, with a population of 147.
There are 9 cities in Mercer County, Ohio.