32 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Marion | 1 | 43,486 | 43,991 | 0.07% | 1,186 | 37 | Township |
| Marion | 2 | 35,456 | 36,053 | -0.34% | 2,735 | 13 | City |
| Marion | 3 | 6,761 | 6,630 | 0.45% | 160 | 42 | Township |
| Marion | 4 | 5,509 | 5,512 | 0.02% | 217 | 25 | Township |
| Pleasant | 5 | 4,989 | 4,866 | 0.67% | 177 | 28 | Township |
| Marion | 6 | 3,373 | 3,332 | 0.24% | 81 | 41 | Township |
| Marion | 7 | 3,316 | 3,133 | 1.34% | 147 | 23 | Township |
| Claridon | 8 | 2,908 | 2,832 | 1.47% | 79 | 37 | Township |
| Marion | 9 | 2,427 | 2,509 | -0.57% | 66 | 37 | Township |
| Marion | 10 | 2,259 | 2,299 | -0.09% | 68 | 33 | Township |
| Montgomery | 11 | 2,087 | 2,080 | 0.58% | 73 | 28 | Township |
| Prospect | 12 | 2,006 | 2,021 | 0.2% | 83 | 24 | Township |
| Richland | 13 | 1,827 | 1,779 | 0.94% | 59 | 31 | Township |
| Grand Prairie | 14 | 1,533 | 1,549 | 0% | 63 | 24 | Township |
| Marion | 15 | 1,476 | 1,487 | 0.07% | 65 | 23 | Township |
| Marion | 16 | 1,286 | 1,278 | 0.16% | 35 | 36 | Township |
| Big Island | 17 | 1,184 | 1,191 | 0.17% | 34 | 35 | Township |
| Marion | 18 | 1,164 | 1,194 | -0.68% | 31 | 38 | Township |
| Waldo | 19 | 1,121 | 1,121 | 0% | 59 | 19 | Township |
| Green Camp | 20 | 1,088 | 1,104 | 0.09% | 45 | 24 | Township |
| Prospect | 21 | 1,053 | 1,073 | -0.38% | 1,454 | 1 | Village |
| Tully | 22 | 863 | 808 | 1.05% | 41 | 21 | Township |
| Marion | 23 | 729 | 733 | -0.14% | 21 | 34 | Township |
| La Rue | 24 | 668 | 683 | -0.45% | 1,397 | 0 | Village |
| Salt Rock | 25 | 610 | 613 | -0.16% | 25 | 25 | Township |
| Marion | 26 | 593 | 600 | -0.84% | 24 | 24 | Township |
| Caledonia | 27 | 556 | 563 | -0.36% | 2,298 | 0 | Village |
| New Bloomington | 28 | 414 | 412 | 0% | 941 | 0 | Village |
| Morral | 29 | 367 | 374 | -0.54% | 136 | 3 | Village |
| Grand | 30 | 347 | 346 | 0.29% | 19 | 18 | Township |
| Waldo | 31 | 315 | 323 | -0.63% | 486 | 1 | Village |
| Green Camp | 32 | 304 | 309 | -0.33% | 899 | 0 | Village |
Marion is the largest city in Marion County, with a population of 43,486.
Green Camp is the smallest city in Marion County, with a population of 304.
There are 32 cities in Marion County, Ohio.