18 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| White River | 1 | 506 | 538 | -1.17% | 971 | 0.52 | City |
| Horse Creek | 2 | 259 | 175 | 7.02% | 273 | 0.95 | CDP |
| Norris township | 3 | 167 | 176 | -1.18% | 8 | 21.31 | Township |
| Norris | 4 | 156 | 148 | 0% | 188 | 0.83 | CDP |
| Blackpipe township | 5 | 47 | 49 | 0% | 1 | 35.94 | Township |
| Wood | 6 | 40 | 42 | 0% | 163 | 0.25 | Town |
| Bad Nation township | 7 | 31 | 32 | 0% | 0.00 | 72.07 | Township |
| Mosher township | 8 | 25 | 26 | 0% | 1 | 35.92 | Township |
| Cody township | 9 | 23 | 24 | 0% | 0.00 | 73.76 | Township |
| Running Bird township | 10 | 20 | 21 | 0% | 1 | 35.91 | Township |
| Red Fish township | 11 | 17 | 18 | 0% | 0.00 | 43.30 | Township |
| Riverside township | 12 | 17 | 18 | 0% | 0.00 | 55.72 | Township |
| Surprise Valley township | 13 | 11 | 14 | -8.33% | 0.00 | 33.51 | Township |
| Ring Thunder township | 14 | 8 | 11 | -11.11% | 0.00 | 35.97 | Township |
| Rocky Ford township | 15 | 8 | 8 | 0% | 0.00 | 50.20 | Township |
| New Surprise Valley township | 16 | 6 | 6 | 0% | 0.00 | 35.74 | Township |
| Prospect township | 17 | 1 | 1 | 0% | 0.00 | 85.73 | Township |
| Butte township | 18 | 0 | 0 | 0.00 | 36.61 | Township |
White River is the largest city in Mellette County, with a population of 506.
Butte township is the smallest city in Mellette County.
There are 18 cities in Mellette County, South Dakota.