| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Rapid City | 1 | 81,888 | 74,947 | 1.61% | 1,463 | 56 | City |
| Box Elder | 2 | 14,424 | 11,948 | 3.5% | 978 | 15 | City |
| Hill City | 3 | 954 | 877 | 1.71% | 727 | 1 | City |
| Wall | 4 | 661 | 695 | -1.05% | 251 | 3 | Town |
| New Underwood | 5 | 594 | 598 | 0% | 357 | 2 | City |
| Keystone | 6 | 272 | 249 | 1.49% | 91 | 3 | Town |
| Quinn | 7 | 61 | 61 | 0% | 51 | 1 | Town |
| Wasta | 8 | 59 | 63 | -1.67% | 307 | 0 | Town |
Rapid City is the largest city in Pennington County, with a population of 81,888.
Wasta is the smallest city in Pennington County, with a population of 59.
There are 8 cities in Pennington County, South Dakota.