8 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Marion | 1 | 35,209 | 36,013 | -0.46% | 2,716 | 12.96 | City |
| Prospect | 2 | 1,041 | 1,068 | -0.48% | 1,438 | 0.72 | Village |
| La Rue | 3 | 665 | 684 | -0.6% | 1,391 | 0.48 | Village |
| Caledonia | 4 | 545 | 557 | -0.37% | 2,252 | 0.24 | Village |
| New Bloomington | 5 | 414 | 413 | 0% | 941 | 0.44 | Village |
| Morral | 6 | 369 | 374 | -0.27% | 137 | 2.70 | Village |
| Waldo | 7 | 312 | 321 | -0.64% | 481 | 0.65 | Village |
| Green Camp | 8 | 300 | 309 | -0.66% | 888 | 0.34 | Village |
Marion is the largest city in Marion County, with a population of 35,209.
Green Camp is the smallest city in Marion County.
There are 8 cities in Marion County, Ohio.