12 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Greensburg | 1 | 12,385 | 12,330 | 0.09% | 1,323 | 9.36 | City |
| Sandcreek township | 2 | 3,082 | 3,116 | -0.19% | 71 | 43.17 | Township |
| Country Squire Lakes | 3 | 2,883 | 3,220 | -1.57% | 1,127 | 2.56 | CDP |
| Fugit township | 4 | 1,862 | 1,879 | -0.16% | 44 | 42.66 | Township |
| Adams township | 5 | 1,815 | 1,836 | -0.22% | 55 | 32.94 | Township |
| Westport | 6 | 1,377 | 1,396 | -0.29% | 1,197 | 1.15 | Town |
| Clay township | 7 | 1,282 | 1,290 | 0% | 25 | 50.65 | Township |
| Saltcreek township | 8 | 1,123 | 1,134 | -0.09% | 38 | 29.86 | Township |
| St. Paul | 9 | 959 | 961 | 0% | 3,273 | 0.29 | Town |
| Jackson township | 10 | 940 | 945 | 0% | 23 | 40.27 | Township |
| New Point | 11 | 316 | 318 | 0% | 1,013 | 0.31 | Town |
| Millhousen | 12 | 146 | 150 | -0.68% | 162 | 0.90 | Town |
Greensburg is the largest city in Decatur County, with a population of 12,385.
Millhousen is the smallest city in Decatur County.
There are 12 cities in Decatur County, Indiana.