26 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Ottawa | 1 | 7,970 | 8,022 | -0.16% | 221 | 36 | Township |
| Ottawa | 2 | 4,393 | 4,450 | -0.25% | 966 | 5 | Village |
| Pleasant | 3 | 3,695 | 3,782 | -0.54% | 102 | 36 | Township |
| Union | 4 | 2,916 | 2,939 | -0.34% | 96 | 30 | Township |
| Riley | 5 | 2,169 | 2,230 | -0.78% | 72 | 30 | Township |
| Leipsic | 6 | 2,153 | 2,188 | -0.32% | 584 | 4 | Village |
| Columbus Grove | 7 | 2,118 | 2,150 | -0.28% | 1,725 | 1 | Village |
| Monterey | 8 | 2,023 | 2,042 | -0.44% | 82 | 25 | Township |
| Jennings | 9 | 1,987 | 2,019 | -0.7% | 71 | 28 | Township |
| Liberty | 10 | 1,661 | 1,672 | -0.18% | 46 | 36 | Township |
| Kalida | 11 | 1,448 | 1,452 | -0.07% | 861 | 2 | Village |
| Greensburg | 12 | 1,440 | 1,427 | 0.21% | 48 | 30 | Township |
| Blanchard | 13 | 1,190 | 1,227 | -0.75% | 33 | 36 | Township |
| Pandora | 14 | 1,182 | 1,197 | -0.25% | 1,109 | 1 | Village |
| Palmer | 15 | 1,162 | 1,152 | -0.09% | 32 | 36 | Township |
| Sugar Creek | 16 | 1,149 | 1,178 | -0.52% | 38 | 30 | Township |
| Continental | 17 | 1,078 | 1,100 | -0.37% | 901 | 1 | Village |
| Glandorf | 18 | 980 | 965 | 0.31% | 564 | 2 | Village |
| Ottoville | 19 | 971 | 968 | 0.1% | 1,025 | 1 | Village |
| Fort Jennings | 20 | 527 | 522 | 0.19% | 936 | 1 | Village |
| Dupont | 21 | 204 | 208 | -0.49% | 223 | 1 | Village |
| Cloverdale | 22 | 165 | 169 | -0.6% | 268 | 1 | Village |
| Gilboa | 23 | 164 | 168 | -0.61% | 1,252 | 0 | Village |
| Vaughnsville | 24 | 133 | 271 | -6.34% | 778 | 0 | CDP |
| Miller City | 25 | 126 | 133 | -0.79% | 318 | 0 | Village |
| Belmore | 26 | 59 | 61 | 0% | 133 | 0 | Village |
Ottawa is the largest city in Putnam County, with a population of 7,970.
Belmore is the smallest city in Putnam County, with a population of 59.
There are 26 cities in Putnam County, Ohio.