10 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Hannibal | 1 | 16,743 | 17,110 | -0.39% | 1,046 | 16 | City |
| Hannibal | 2 | 16,743 | 17,073 | -0.39% | 1,046 | 16 | City |
| Palmyra | 3 | 3,650 | 3,621 | 0.16% | 1,176 | 3 | City |
| Palmyra | 4 | 3,650 | 3,619 | 0.16% | 1,176 | 3 | City |
| Philadelphia | 5 | 378 | 186 | 7.39% | 499 | 1 | CDP |
| Rensselaer | 6 | 253 | 251 | 0% | 129 | 2 | Village |
| Rensselaer | 7 | 253 | 251 | 0% | 129 | 2 | Village |
| Sundown | 8 | 199 | 106 | 6.99% | 136 | 1 | CDP |
| Taylor | 9 | 141 | 141 | 0% | 8 | 17 | Township |
| Taylor | 10 | 141 | 140 | 0% | 8 | 17 | Township |
Hannibal is the largest city in Marion County, with a population of 16,743.
Taylor is the smallest city in Marion County, with a population of 141.
There are 10 cities in Marion County, Missouri.