26 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Oberlin | 1 | 1,585 | 1,634 | -0.63% | 830 | 1.91 | City |
| Dresden township | 2 | 293 | 327 | -2.33% | 8 | 36.05 | Township |
| Norcatur | 3 | 156 | 161 | -0.64% | 157 | 1 | City |
| Jennings township | 4 | 110 | 110 | 0.92% | 3 | 35.74 | Township |
| Dresden township | 5 | 99 | 100 | 1.02% | 3 | 35.68 | Township |
| Jennings | 6 | 80 | 82 | 0% | 299 | 0.27 | City |
| Oberlin township | 7 | 76 | 75 | 1.33% | 2 | 34.26 | Township |
| Beaver township | 8 | 71 | 70 | 1.43% | 2 | 35.69 | Township |
| Center township | 9 | 54 | 55 | 0% | 2 | 35.80 | Township |
| Olive township | 10 | 51 | 52 | 0% | 1 | 35.42 | Township |
| Dresden | 11 | 42 | 44 | 0% | 47 | 0.90 | City |
| Finley township | 12 | 36 | 37 | 0% | 1 | 35.73 | Township |
| Harlan township | 13 | 35 | 36 | 0% | 1 | 35.63 | Township |
| Custer township | 14 | 33 | 34 | 0% | 1 | 35.73 | Township |
| Allison township | 15 | 32 | 33 | 0% | 1 | 35.84 | Township |
| Prairie Dog township | 16 | 32 | 33 | 0% | 1 | 35.77 | Township |
| Bassettville township | 17 | 31 | 29 | 3.33% | 1 | 35.83 | Township |
| Sappa township | 18 | 25 | 23 | 4.17% | 1 | 35.99 | Township |
| Summit township | 19 | 24 | 22 | 4.35% | 1 | 35.85 | Township |
| Pleasant Valley township | 20 | 23 | 22 | 0% | 1 | 35.74 | Township |
| Cook township | 21 | 20 | 20 | 0% | 1 | 35.87 | Township |
| Altory township | 22 | 19 | 19 | 0% | 1 | 35.79 | Township |
| Sherman township | 23 | 16 | 16 | 0% | 0.00 | 35.64 | Township |
| Grant township | 24 | 15 | 15 | 0% | 0.00 | 35.63 | Township |
| Lyon township | 25 | 13 | 13 | 0% | 0.00 | 35.91 | Township |
| Roosevelt township | 26 | 11 | 11 | 0% | 0.00 | 35.89 | Township |
Oberlin is the largest city in Decatur County, with a population of 1,585.
Roosevelt township is the smallest city in Decatur County.
There are 26 cities in Decatur County, Kansas.