9 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Pella | 1 | 11,211 | 10,472 | 1.11% | 1,200 | 9 | City |
| Knoxville | 2 | 7,373 | 7,574 | -0.45% | 1,597 | 5 | City |
| Pleasantville | 3 | 1,701 | 1,686 | 0.18% | 695 | 2 | City |
| Melcher-Dallas | 4 | 1,191 | 1,196 | -0.08% | 1,145 | 1 | City |
| Bussey | 5 | 377 | 380 | 0% | 1,212 | 0 | City |
| Harvey | 6 | 245 | 235 | 0.82% | 362 | 1 | City |
| Hamilton | 7 | 127 | 121 | 0.79% | 251 | 1 | City |
| Swan | 8 | 80 | 76 | 1.27% | 130 | 1 | City |
| Marysville | 9 | 46 | 45 | 0% | 85 | 1 | City |
Pella is the largest city in Marion County, with a population of 11,211.
Marysville is the smallest city in Marion County, with a population of 46.
There are 9 cities in Marion County, Iowa.