26 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Oberlin | 1 | 1,605 | 1,628 | -0.31% | 840 | 2 | City |
| Dresden | 2 | 293 | 327 | -2.98% | 8 | 36 | Township |
| Norcatur | 3 | 159 | 162 | -0.63% | 160 | 1 | City |
| Jennings | 4 | 105 | 108 | -0.94% | 3 | 36 | Township |
| Dresden | 5 | 98 | 102 | -1.01% | 3 | 36 | Township |
| Jennings | 6 | 78 | 81 | -1.27% | 291 | 0 | City |
| Oberlin | 7 | 78 | 79 | 0% | 2 | 34 | Township |
| Beaver | 8 | 64 | 66 | -1.54% | 2 | 36 | Township |
| Center | 9 | 52 | 54 | -1.89% | 1 | 36 | Township |
| Olive | 10 | 50 | 52 | -1.96% | 1 | 35 | Township |
| Dresden | 11 | 42 | 44 | -2.33% | 47 | 1 | City |
| Finley | 12 | 37 | 39 | -2.63% | 1 | 36 | Township |
| Allison | 13 | 34 | 34 | 0% | 1 | 36 | Township |
| Harlan | 14 | 34 | 36 | -2.86% | 1 | 36 | Township |
| Custer | 15 | 33 | 33 | 0% | 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 1,605.
Roosevelt is the smallest city in Decatur County, with a population of 12.
There are 26 cities in Decatur County, Kansas.