11 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Greensburg | 1 | 12,313 | 12,330 | -0.03% | 1,315 | 9 | City |
| Sandcreek | 2 | 3,119 | 3,114 | 0.42% | 72 | 43 | Township |
| Fugit | 3 | 1,882 | 1,884 | 0.37% | 44 | 43 | Township |
| Adams | 4 | 1,840 | 1,836 | 0.44% | 56 | 33 | Township |
| Westport | 5 | 1,390 | 1,394 | -0.07% | 1,156 | 1 | Town |
| Clay | 6 | 1,294 | 1,288 | 0.54% | 26 | 51 | Township |
| Saltcreek | 7 | 1,131 | 1,136 | 0.27% | 38 | 30 | Township |
| St. Paul | 8 | 967 | 962 | 0.1% | 3,300 | 0 | Town |
| Jackson | 9 | 947 | 946 | 0.42% | 24 | 40 | Township |
| New Point | 10 | 315 | 318 | -0.32% | 1,010 | 0 | Town |
| Millhousen | 11 | 147 | 147 | 0% | 163 | 1 | Town |
Greensburg is the largest city in Decatur County, with a population of 12,313.
Millhousen is the smallest city in Decatur County, with a population of 147.
There are 11 cities in Decatur County, Indiana.