18 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Guttenberg | 1 | 1,804 | 1,814 | -0.11% | 822 | 2.19 | City |
| Monona | 2 | 1,461 | 1,471 | -0.14% | 1,073 | 1.36 | City |
| Elkader | 3 | 1,186 | 1,213 | -0.42% | 868 | 1.37 | City |
| Strawberry Point | 4 | 1,140 | 1,157 | -0.26% | 546 | 2.09 | City |
| Edgewood | 5 | 911 | 908 | 0.11% | 949 | 0.96 | City |
| Garnavillo | 6 | 747 | 756 | -0.27% | 791 | 0.94 | City |
| McGregor | 7 | 718 | 735 | -0.42% | 555 | 1.29 | City |
| Marquette | 8 | 434 | 428 | 0.23% | 234 | 1.86 | City |
| Luana | 9 | 306 | 301 | 0.33% | 278 | 1.10 | City |
| Farmersburg | 10 | 262 | 272 | -0.76% | 644 | 0.41 | City |
| Volga | 11 | 199 | 203 | -0.5% | 265 | 0.75 | City |
| North Buena Vista | 12 | 109 | 106 | 0.93% | 117 | 0.93 | City |
| St. Olaf | 13 | 101 | 103 | 0% | 419 | 0.24 | City |
| Balltown | 14 | 79 | 79 | 0% | 1,097 | 0.07 | City |
| Garber | 15 | 78 | 80 | 0% | 347 | 0.23 | City |
| Clayton | 16 | 46 | 46 | 0% | 89 | 0.51 | City |
| Osterdock | 17 | 42 | 44 | 0% | 106 | 0.40 | City |
| Elkport | 18 | 28 | 28 | 0% | 112 | 0.25 | City |
Guttenberg is the largest city in Clayton County, with a population of 1,804.
Elkport is the smallest city in Clayton County.
There are 18 cities in Clayton County, Iowa.