18 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Guttenberg | 1 | 1,802 | 1,812 | -0.11% | 821 | 2 | City |
| Monona | 2 | 1,459 | 1,474 | -0.21% | 1,071 | 1 | City |
| Elkader | 3 | 1,186 | 1,214 | -0.5% | 868 | 1 | City |
| Strawberry Point | 4 | 1,136 | 1,158 | -0.44% | 544 | 2 | City |
| Edgewood | 5 | 908 | 907 | 0% | 946 | 1 | City |
| Garnavillo | 6 | 748 | 760 | -0.4% | 792 | 1 | City |
| McGregor | 7 | 721 | 738 | -0.55% | 557 | 1 | City |
| Marquette | 8 | 435 | 427 | 0.23% | 234 | 2 | City |
| Luana | 9 | 303 | 301 | 0% | 275 | 1 | City |
| Farmersburg | 10 | 262 | 270 | -0.76% | 644 | 0 | City |
| Volga | 11 | 199 | 203 | -0.5% | 265 | 1 | City |
| North Buena Vista | 12 | 107 | 106 | 0% | 115 | 1 | City |
| St. Olaf | 13 | 101 | 104 | -0.98% | 419 | 0 | City |
| Balltown | 14 | 78 | 78 | 0% | 1,083 | 0 | City |
| Garber | 15 | 75 | 77 | -1.32% | 333 | 0 | City |
| Clayton | 16 | 44 | 46 | -2.22% | 86 | 1 | City |
| Osterdock | 17 | 44 | 46 | -2.22% | 111 | 0 | City |
| Elkport | 18 | 29 | 29 | 0% | 116 | 0 | City |
Guttenberg is the largest city in Clayton County, with a population of 1,802.
Elkport is the smallest city in Clayton County, with a population of 29.
There are 18 cities in Clayton County, Iowa.