10 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Spencer | 1 | 11,549 | 11,303 | 0.43% | 1,055 | 10.95 | City |
| Everly | 2 | 571 | 573 | 0% | 545 | 1.05 | City |
| Royal | 3 | 380 | 380 | 0% | 1,288 | 0.29 | City |
| Peterson | 4 | 319 | 319 | 0% | 615 | 0.52 | City |
| Fostoria | 5 | 229 | 231 | 0% | 564 | 0.41 | City |
| Dickens | 6 | 147 | 146 | 0% | 176 | 0.83 | City |
| Webb | 7 | 138 | 140 | 0% | 274 | 0.50 | City |
| Greenville | 8 | 68 | 68 | 0% | 410 | 0.17 | City |
| Rossie | 9 | 47 | 47 | 0% | 326 | 0.14 | City |
| Gillett Grove | 10 | 32 | 32 | 0% | 144 | 0.22 | City |
Spencer is the largest city in Clay County, with a population of 11,549.
Gillett Grove is the smallest city in Clay County.
There are 10 cities in Clay County, Iowa.