26 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Oberlin | 1 | 1,601 | 1,628 | -0.25% | 838 | 2 | City |
| Dresden | 2 | 284 | 327 | -3.07% | 8 | 36 | Township |
| Norcatur | 3 | 159 | 162 | 0% | 160 | 1 | City |
| Jennings | 4 | 104 | 108 | -0.95% | 3 | 36 | Township |
| Dresden | 5 | 97 | 102 | -1.02% | 3 | 36 | Township |
| Oberlin | 6 | 78 | 79 | 0% | 2 | 34 | Township |
| Jennings | 7 | 78 | 81 | 0% | 291 | 0 | City |
| Beaver | 8 | 63 | 66 | -1.56% | 2 | 36 | Township |
| Center | 9 | 51 | 54 | -1.92% | 1 | 36 | Township |
| Olive | 10 | 49 | 52 | -2% | 1 | 35 | Township |
| Dresden | 11 | 42 | 44 | 0% | 47 | 1 | City |
| Finley | 12 | 36 | 39 | -2.7% | 1 | 36 | Township |
| Allison | 13 | 34 | 34 | 0% | 1 | 36 | Township |
| Custer | 14 | 33 | 33 | 0% | 1 | 36 | Township |
| Harlan | 15 | 33 | 36 | -2.94% | 1 | 36 | Township |
| Prairie Dog | 16 | 32 | 32 | 0% | 1 | 36 | Township |
| Bassettville | 17 | 30 | 30 | 0% | 1 | 36 | Township |
| Sappa | 18 | 22 | 22 | 0% | 1 | 36 | Township |
| Cook | 19 | 20 | 20 | 0% | 1 | 36 | Township |
| Sherman | 20 | 19 | 19 | 0% | 1 | 36 | Township |
| Summit | 21 | 19 | 19 | 0% | 1 | 36 | Township |
| Altory | 22 | 18 | 17 | 0% | 1 | 36 | Township |
| Pleasant Valley | 23 | 17 | 17 | 0% | 0.00 | 36 | Township |
| Grant | 24 | 14 | 14 | 0% | 0.00 | 36 | Township |
| Lyon | 25 | 13 | 13 | 0% | 0.00 | 36 | Township |
| Roosevelt | 26 | 12 | 12 | 0% | 0.00 | 36 | Township |
Oberlin is the largest city in Decatur County, with a population of 1,601.
Roosevelt is the smallest city in Decatur County, with a population of 12.
There are 26 cities in Decatur County, Kansas.