16 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| St. James | 1 | 4,724 | 4,802 | -0.27% | 2,025 | 2 | City |
| Madelia | 2 | 2,446 | 2,397 | 0.33% | 1,618 | 2 | City |
| Butterfield | 3 | 595 | 600 | -0.17% | 1,469 | 0 | City |
| Madelia | 4 | 302 | 303 | 0% | 9 | 33 | Township |
| Riverdale | 5 | 285 | 284 | 0% | 7 | 39 | Township |
| Rosendale | 6 | 270 | 271 | 0% | 7 | 38 | Township |
| Antrim | 7 | 265 | 266 | 0% | 7 | 36 | Township |
| South Branch | 8 | 252 | 254 | 0% | 6 | 39 | Township |
| St. James | 9 | 226 | 228 | 0% | 7 | 34 | Township |
| Lewisville | 10 | 207 | 206 | 0% | 845 | 0 | City |
| Fieldon | 11 | 205 | 206 | 0% | 6 | 36 | Township |
| Butterfield | 12 | 198 | 199 | 0% | 6 | 35 | Township |
| Odin | 13 | 159 | 164 | -1.24% | 5 | 35 | Township |
| Odin | 14 | 123 | 125 | 0% | 332 | 0 | City |
| Darfur | 15 | 82 | 84 | 0% | 358 | 0 | City |
| La Salle | 16 | 75 | 75 | 0% | 862 | 0 | City |
St. James is the largest city in Watonwan County, with a population of 4,724.
La Salle is the smallest city in Watonwan County, with a population of 75.
There are 16 cities in Watonwan County, Minnesota.