10 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Spencer | 1 | 11,446 | 11,304 | 0.25% | 1,045 | 11 | City |
| Everly | 2 | 569 | 572 | -0.18% | 543 | 1 | City |
| Royal | 3 | 378 | 380 | -0.26% | 1,281 | 0 | City |
| Peterson | 4 | 321 | 320 | 0% | 618 | 1 | City |
| Fostoria | 5 | 228 | 231 | -0.44% | 562 | 0 | City |
| Dickens | 6 | 146 | 145 | 0% | 175 | 1 | City |
| Webb | 7 | 138 | 140 | -0.72% | 274 | 1 | City |
| Greenville | 8 | 69 | 69 | 0% | 416 | 0 | City |
| Rossie | 9 | 46 | 46 | 0% | 319 | 0 | City |
| Gillett Grove | 10 | 31 | 31 | 0% | 140 | 0 | City |
Spencer is the largest city in Clay County, with a population of 11,446.
Gillett Grove is the smallest city in Clay County, with a population of 31.
There are 10 cities in Clay County, Iowa.