3 cities
| City | Rank | 2026 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Thayer | 1 | 1,916 | 1,879 | 0.31% | 784 | 2 | City |
| Alton | 2 | 703 | 700 | 0.14% | 448 | 2 | City |
| Koshkonong | 3 | 197 | 194 | 0.51% | 1,101 | 0 | Town |
Thayer is the largest city in Oregon County, with a population of 1,916.
Koshkonong is the smallest city in Oregon County, with a population of 197.
There are 3 cities in Oregon County, Missouri.