5 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Greensburg | 1 | 12,310 | 12,330 | -0.02% | 1,315 | 9 | City |
| Westport | 2 | 1,389 | 1,394 | -0.07% | 1,156 | 1 | Town |
| St. Paul | 3 | 968 | 962 | 0.1% | 3,304 | 0 | Town |
| New Point | 4 | 315 | 318 | 0% | 1,010 | 0 | Town |
| Millhousen | 5 | 147 | 147 | 0% | 163 | 1 | Town |
Greensburg is the largest city in Decatur County, with a population of 12,310.
Millhousen is the smallest city in Decatur County, with a population of 147.
There are 5 cities in Decatur County, Indiana.