9 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Pella | 1 | 11,055 | 10,467 | 1.08% | 1,183 | 9.34 | City |
| Knoxville | 2 | 7,340 | 7,570 | -0.62% | 1,589 | 4.62 | City |
| Pleasantville | 3 | 1,690 | 1,689 | 0% | 691 | 2.45 | City |
| Melcher-Dallas | 4 | 1,176 | 1,196 | -0.34% | 1,131 | 1.04 | City |
| Bussey | 5 | 370 | 379 | -0.54% | 1,190 | 0.31 | City |
| Harvey | 6 | 241 | 236 | 0.42% | 356 | 0.68 | City |
| Hamilton | 7 | 128 | 125 | 0.79% | 253 | 0.51 | City |
| Swan | 8 | 77 | 76 | 0% | 125 | 0.62 | City |
| Marysville | 9 | 47 | 46 | 0% | 87 | 0.54 | City |
Pella is the largest city in Marion County, with a population of 11,055.
Marysville is the smallest city in Marion County.
There are 9 cities in Marion County, Iowa.