| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Marion | 1 | 35,449 | 36,057 | -0.39% | 2,734 | 13 | City |
| Prospect | 2 | 1,051 | 1,072 | -0.47% | 1,452 | 1 | Village |
| La Rue | 3 | 671 | 682 | -0.45% | 1,404 | 0 | Village |
| Caledonia | 4 | 557 | 562 | -0.36% | 2,302 | 0 | Village |
| New Bloomington | 5 | 418 | 414 | 0% | 950 | 0 | Village |
| Morral | 6 | 365 | 374 | -0.54% | 135 | 3 | Village |
| Waldo | 7 | 318 | 322 | -0.63% | 491 | 1 | Village |
| Green Camp | 8 | 303 | 309 | -0.66% | 896 | 0 | Village |
Marion is the largest city in Marion County, with a population of 35,449.
Green Camp is the smallest city in Marion County, with a population of 303.
There are 8 cities in Marion County, Ohio.