8 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Marion | 1 | 35,337 | 36,053 | -0.34% | 2,726 | 13 | City |
| Prospect | 2 | 1,049 | 1,073 | -0.38% | 1,449 | 1 | Village |
| La Rue | 3 | 665 | 683 | -0.45% | 1,391 | 0 | Village |
| Caledonia | 4 | 555 | 563 | -0.18% | 2,293 | 0 | Village |
| New Bloomington | 5 | 415 | 412 | 0.24% | 943 | 0 | Village |
| Morral | 6 | 366 | 374 | -0.27% | 136 | 3 | Village |
| Waldo | 7 | 314 | 323 | -0.32% | 485 | 1 | Village |
| Green Camp | 8 | 303 | 309 | -0.33% | 896 | 0 | Village |
Marion is the largest city in Marion County, with a population of 35,337.
Green Camp is the smallest city in Marion County, with a population of 303.
There are 8 cities in Marion County, Ohio.