| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| St. James | 1 | 4,866 | 4,805 | 0.06% | 2,086 | 2 | City |
| Madelia | 2 | 2,504 | 2,399 | 0.64% | 1,656 | 2 | City |
| Butterfield | 3 | 612 | 600 | 0.16% | 1,511 | 0 | City |
| Lewisville | 4 | 208 | 205 | 0% | 849 | 0 | City |
| Odin | 5 | 127 | 125 | 0% | 343 | 0 | City |
| Darfur | 6 | 84 | 84 | 0% | 367 | 0 | City |
| La Salle | 7 | 75 | 74 | 0% | 862 | 0 | City |
St. James is the largest city in Watonwan County, with a population of 4,866.
La Salle is the smallest city in Watonwan County, with a population of 75.
There are 7 cities in Watonwan County, Minnesota.