18 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Genoa | 1 | 28,509 | 24,945 | 2% | 1,609 | 18 | Township |
| Port Clinton | 2 | 5,889 | 6,016 | -0.44% | 2,763 | 2 | City |
| Danbury | 3 | 4,852 | 4,919 | -0.25% | 268 | 18 | Township |
| Clay | 4 | 4,709 | 4,809 | -0.34% | 181 | 26 | Township |
| Allen | 5 | 3,680 | 3,763 | -0.38% | 146 | 25 | Township |
| Catawba Island | 6 | 3,647 | 3,705 | -0.27% | 651 | 6 | Township |
| Harris | 7 | 2,865 | 2,936 | -0.42% | 101 | 28 | Township |
| Oak Harbor | 8 | 2,782 | 2,819 | -0.29% | 1,753 | 2 | Village |
| Benton | 9 | 2,363 | 2,417 | -0.42% | 53 | 44 | Township |
| Genoa | 10 | 2,176 | 2,224 | -0.46% | 1,089 | 2 | Village |
| Elmore | 11 | 1,364 | 1,399 | -0.51% | 1,475 | 1 | Village |
| Erie | 12 | 1,158 | 1,163 | -0.17% | 95 | 12 | Township |
| Bay | 13 | 1,111 | 1,127 | -0.27% | 69 | 16 | Township |
| Marblehead | 14 | 831 | 849 | -0.48% | 262 | 3 | Village |
| Put-in-Bay | 15 | 791 | 807 | -0.25% | 160 | 5 | Township |
| Rocky Ridge | 16 | 305 | 310 | -0.33% | 304 | 1 | Village |
| Clay Center | 17 | 245 | 259 | -1.21% | 242 | 1 | Village |
| Put-in-Bay | 18 | 151 | 155 | -0.66% | 344 | 0 | Village |
Genoa is the largest city in Ottawa County, with a population of 28,509.
Put-in-Bay is the smallest city in Ottawa County, with a population of 151.
There are 18 cities in Ottawa County, Ohio.