32 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Marion | 1 | 43,515 | 43,991 | 0.07% | 1,187 | 37 | Township |
| Marion | 2 | 35,337 | 36,053 | -0.34% | 2,726 | 13 | City |
| Marion | 3 | 6,791 | 6,630 | 0.44% | 160 | 42 | Township |
| Marion | 4 | 5,510 | 5,512 | 0.02% | 217 | 25 | Township |
| Pleasant | 5 | 5,022 | 4,866 | 0.66% | 178 | 28 | Township |
| Marion | 6 | 3,381 | 3,332 | 0.24% | 82 | 41 | Township |
| Marion | 7 | 3,360 | 3,133 | 1.33% | 148 | 23 | Township |
| Claridon | 8 | 2,950 | 2,832 | 1.44% | 80 | 37 | Township |
| Marion | 9 | 2,413 | 2,509 | -0.58% | 65 | 37 | Township |
| Marion | 10 | 2,257 | 2,299 | -0.09% | 68 | 33 | Township |
| Montgomery | 11 | 2,099 | 2,080 | 0.57% | 74 | 28 | Township |
| Prospect | 12 | 2,010 | 2,021 | 0.2% | 83 | 24 | Township |
| Richland | 13 | 1,844 | 1,779 | 0.93% | 60 | 31 | Township |
| Grand Prairie | 14 | 1,533 | 1,549 | 0% | 63 | 24 | Township |
| Marion | 15 | 1,477 | 1,487 | 0.07% | 65 | 23 | Township |
| Marion | 16 | 1,288 | 1,278 | 0.16% | 36 | 36 | Township |
| Big Island | 17 | 1,186 | 1,191 | 0.17% | 34 | 35 | Township |
| Marion | 18 | 1,156 | 1,194 | -0.69% | 31 | 38 | Township |
| Waldo | 19 | 1,121 | 1,121 | 0% | 59 | 19 | Township |
| Green Camp | 20 | 1,089 | 1,104 | 0.09% | 45 | 24 | Township |
| Prospect | 21 | 1,049 | 1,073 | -0.38% | 1,449 | 1 | Village |
| Tully | 22 | 872 | 808 | 1.04% | 41 | 21 | Township |
| Marion | 23 | 728 | 733 | -0.14% | 21 | 34 | Township |
| La Rue | 24 | 665 | 683 | -0.45% | 1,391 | 0 | Village |
| Salt Rock | 25 | 609 | 613 | -0.16% | 25 | 25 | Township |
| Marion | 26 | 588 | 600 | -0.84% | 24 | 24 | Township |
| Caledonia | 27 | 555 | 563 | -0.18% | 2,293 | 0 | Village |
| New Bloomington | 28 | 415 | 412 | 0.24% | 943 | 0 | Village |
| Morral | 29 | 366 | 374 | -0.27% | 136 | 3 | Village |
| Grand | 30 | 348 | 346 | 0.29% | 19 | 18 | Township |
| Waldo | 31 | 314 | 323 | -0.32% | 485 | 1 | Village |
| Green Camp | 32 | 303 | 309 | -0.33% | 896 | 0 | Village |
Marion is the largest city in Marion County, with a population of 43,515.
Green Camp is the smallest city in Marion County, with a population of 303.
There are 32 cities in Marion County, Ohio.