| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Atlantic | 1 | 6,656 | 6,781 | -0.3% | 803 | 8 | City |
| Griswold | 2 | 968 | 990 | -0.41% | 1,589 | 1 | City |
| Anita | 3 | 946 | 961 | -0.32% | 533 | 2 | City |
| Lewis | 4 | 353 | 358 | -0.28% | 699 | 1 | City |
| Massena | 5 | 349 | 356 | -0.57% | 509 | 1 | City |
| Cumberland | 6 | 247 | 248 | 0% | 398 | 1 | City |
| Marne | 7 | 107 | 108 | -0.93% | 191 | 1 | City |
| Wiota | 8 | 92 | 92 | 0% | 308 | 0 | City |
Atlantic is the largest city in Cass County, with a population of 6,656.
Wiota is the smallest city in Cass County, with a population of 92.
There are 8 cities in Cass County, Iowa.