| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Atlantic | 1 | 6,684 | 6,782 | -0.24% | 806 | 8 | City |
| Griswold | 2 | 968 | 988 | -0.31% | 1,589 | 1 | City |
| Anita | 3 | 949 | 960 | -0.21% | 535 | 2 | City |
| Lewis | 4 | 357 | 359 | 0% | 707 | 1 | City |
| Massena | 5 | 350 | 356 | -0.28% | 511 | 1 | City |
| Cumberland | 6 | 248 | 248 | 0% | 400 | 1 | City |
| Marne | 7 | 109 | 108 | 0% | 194 | 1 | City |
| Wiota | 8 | 90 | 92 | 0% | 301 | 0 | City |
Atlantic is the largest city in Cass County, with a population of 6,684.
Wiota is the smallest city in Cass County, with a population of 90.
There are 8 cities in Cass County, Iowa.