3 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Thayer | 1 | 1,913 | 1,875 | 0.42% | 783 | 2.44 | City |
| Alton | 2 | 707 | 701 | 0.14% | 451 | 1.57 | City |
| Koshkonong | 3 | 200 | 195 | 0.5% | 1,117 | 0.18 | Town |
Thayer is the largest city in Oregon County, with a population of 1,913.
Koshkonong is the smallest city in Oregon County.
There are 3 cities in Oregon County, Missouri.