16 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| St. James | 1 | 4,639 | 4,789 | -0.64% | 1,988 | 2.33 | City |
| Madelia | 2 | 2,358 | 2,400 | -0.34% | 1,560 | 1.51 | City |
| Butterfield | 3 | 586 | 601 | -0.51% | 1,447 | 0.41 | City |
| Madelia township | 4 | 299 | 303 | -0.33% | 9 | 33.26 | Township |
| Riverdale township | 5 | 281 | 285 | -0.35% | 7 | 38.85 | Township |
| Rosendale township | 6 | 266 | 272 | -0.37% | 7 | 38.18 | Township |
| Antrim township | 7 | 255 | 265 | -1.16% | 7 | 35.73 | Township |
| South Branch township | 8 | 248 | 252 | 0% | 6 | 39.07 | Township |
| St. James township | 9 | 240 | 244 | 0% | 7 | 33.55 | Township |
| Fieldon township | 10 | 200 | 206 | -0.5% | 6 | 35.74 | Township |
| Lewisville | 11 | 199 | 206 | -0.5% | 812 | 0.24 | City |
| Butterfield township | 12 | 198 | 199 | 0% | 6 | 35.46 | Township |
| Odin township | 13 | 159 | 164 | -0.63% | 5 | 34.69 | Township |
| Odin | 14 | 121 | 125 | -0.82% | 327 | 0.37 | City |
| Darfur | 15 | 81 | 83 | 0% | 354 | 0.23 | City |
| La Salle | 16 | 74 | 76 | 0% | 851 | 0.09 | City |
St. James is the largest city in Watonwan County, with a population of 4,639.
La Salle is the smallest city in Watonwan County.
There are 16 cities in Watonwan County, Minnesota.