| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Greensburg | 1 | 12,319 | 12,329 | 0.03% | 1,316 | 9 | City |
| Westport | 2 | 1,406 | 1,394 | 0% | 1,170 | 1 | Town |
| St. Paul | 3 | 976 | 961 | 0.21% | 3,331 | 0 | Town |
| New Point | 4 | 318 | 318 | -0.31% | 1,019 | 0 | Town |
| Millhousen | 5 | 145 | 145 | 0% | 161 | 1 | Town |
Greensburg is the largest city in Decatur County, with a population of 12,319.
Millhousen is the smallest city in Decatur County, with a population of 145.
There are 5 cities in Decatur County, Indiana.