10 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Lamoni | 1 | 2,069 | 2,082 | -0.14% | 524 | 4 | City |
| Leon | 2 | 1,771 | 1,810 | -0.45% | 565 | 3 | City |
| Grand River | 3 | 191 | 195 | -0.52% | 1,011 | 0 | City |
| Davis City | 4 | 177 | 180 | -0.56% | 305 | 1 | City |
| Decatur | 5 | 174 | 174 | 0% | 460 | 0 | City |
| Van Wert | 6 | 174 | 177 | -0.57% | 489 | 0 | City |
| Garden Grove | 7 | 172 | 174 | -0.58% | 254 | 1 | City |
| Weldon | 8 | 133 | 138 | -0.75% | 686 | 0 | City |
| Pleasanton | 9 | 32 | 32 | 0% | 91 | 0 | City |
| Le Roy | 10 | 10 | 10 | 0% | 26 | 0 | City |
Lamoni is the largest city in Decatur County, with a population of 2,069.
Le Roy is the smallest city in Decatur County, with a population of 10.
There are 10 cities in Decatur County, Iowa.