6 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Annual Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Thayer | 1 | 1,910 | 1,885 | 0.32% | 782 | 2 | City |
| Thayer | 2 | 1,910 | 1,879 | 0.32% | 782 | 2 | City |
| Alton | 3 | 702 | 702 | 0% | 447 | 2 | City |
| Alton | 4 | 702 | 700 | 0% | 447 | 2 | City |
| Koshkonong | 5 | 196 | 195 | 0% | 1,095 | 0 | Town |
| Koshkonong | 6 | 196 | 194 | 0% | 1,095 | 0 | Town |
Thayer is the largest city in Oregon County, with a population of 1,910.
Koshkonong is the smallest city in Oregon County, with a population of 196.
There are 6 cities in Oregon County, Missouri.