23 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Lower Brule | 1 | 962 | 971 | 2.56% | 2,650 | 0 | CDP |
| West Brule | 2 | 664 | 383 | 7.1% | 562 | 1 | CDP |
| Presho | 3 | 466 | 472 | -0.21% | 694 | 1 | City |
| Presho | 4 | 466 | 470 | -0.21% | 694 | 1 | City |
| Oacoma | 5 | 393 | 386 | 0.26% | 150 | 3 | Town |
| Oacoma | 6 | 393 | 386 | 0.26% | 150 | 3 | Town |
| Kennebec | 7 | 286 | 279 | 0.35% | 335 | 1 | Town |
| Kennebec | 8 | 286 | 278 | 0.35% | 335 | 1 | Town |
| Reliance | 9 | 127 | 126 | 0% | 117 | 1 | Town |
| Reliance | 10 | 127 | 125 | 0% | 117 | 1 | Town |
| Vivian | 11 | 125 | 124 | 0% | 3 | 36 | Township |
| Vivian | 12 | 125 | 123 | 0% | 3 | 36 | Township |
| Oacoma | 13 | 81 | 82 | 0% | 1 | 60 | Township |
| Oacoma | 14 | 81 | 82 | 0% | 1 | 60 | Township |
| Iona | 15 | 65 | 65 | 0% | 1 | 128 | Township |
| Iona | 16 | 65 | 65 | 0% | 1 | 128 | Township |
| Vivian | 17 | 33 | 87 | -13.16% | 19 | 2 | CDP |
| Rex | 18 | 23 | 23 | 0% | 1 | 36 | Township |
| Rex | 19 | 23 | 23 | 0% | 1 | 36 | Township |
| Pratt | 20 | 18 | 18 | 0% | 1 | 26 | Township |
| Pratt | 21 | 18 | 18 | 0% | 1 | 26 | Township |
| Bailey | 22 | 12 | 12 | 0% | 0.00 | 43 | Township |
| Bailey | 23 | 12 | 12 | 0% | 0.00 | 43 | Township |
Lower Brule is the largest city in Lyman County, with a population of 962.
Bailey is the smallest city in Lyman County, with a population of 12.
There are 23 cities in Lyman County, South Dakota.