9 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Pella | 1 | 11,088 | 10,472 | 1.12% | 1,187 | 9 | City |
| Knoxville | 2 | 7,406 | 7,574 | -0.46% | 1,604 | 5 | City |
| Pleasantville | 3 | 1,698 | 1,686 | 0.12% | 694 | 2 | City |
| Melcher-Dallas | 4 | 1,192 | 1,196 | -0.08% | 1,146 | 1 | City |
| Bussey | 5 | 377 | 380 | -0.26% | 1,212 | 0 | City |
| Harvey | 6 | 243 | 235 | 0.41% | 359 | 1 | City |
| Hamilton | 7 | 126 | 121 | 0.8% | 249 | 1 | City |
| Swan | 8 | 79 | 76 | 0% | 128 | 1 | City |
| Marysville | 9 | 46 | 45 | 0% | 85 | 1 | City |
Pella is the largest city in Marion County, with a population of 11,088.
Marysville is the smallest city in Marion County, with a population of 46.
There are 9 cities in Marion County, Iowa.