Note: As defined by the US Census Bureau, a city's official boundaries often extend miles beyond the city itself and may even cross county lines. As such, several thousand US cities officially exist in two or more counties (and therefore appear on multiple counties' lists of cities.)
City | Rank | 2024 Pop. | 2020 Pop. | Change | Density (/mi²) | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Lamoni | 1 | 1,979 | 1,957 | 0.25% | 501 | 4.0 | City |
| Leon | 2 | 1,819 | 1,811 | 0.11% | 581 | 3.1 | City |
| Grand River | 3 | 197 | 197 | 0% | 1,042 | 0.2 | City |
| Davis City | 4 | 179 | 177 | 0% | 308 | 0.6 | City |
| Van Wert | 5 | 179 | 177 | 0% | 503 | 0.4 | City |
| Decatur | 6 | 178 | 176 | 0% | 471 | 0.4 | City |
| Garden Grove | 7 | 174 | 172 | 0% | 257 | 0.7 | City |
| Weldon | 8 | 138 | 136 | 0% | 711 | 0.2 | City |
| Pleasanton | 9 | 30 | 30 | 0% | 85 | 0.4 | City |
| Le Roy | 10 | 12 | 12 | 0% | 32 | 0.4 | City |
Note: City markers shown outside the county boundary mean that a part of the city extends into this county, but is primarily located in an adjacent county.
Lamoni is the largest city in Decatur County.
Le Roy is the smallest city in Decatur County.
There are 10 cities in Decatur County, Iowa.