Admitted to the Union on February 14, 1859 as the 33rd state. Oregon Territory was created in 1848.
- 1850 – 1940 federal censuses extant for all counties except for 1890.
| Baker | Benton | Clackamas | Clatsop |
| Columbia | Coos | Crook | Curry |
| Deschutes | Douglas | Gilliam | Grant |
| Harney | Hood River | Jackson | Jefferson |
| Josephine | Klamath | Lake | Lane |
| Lincoln | Linn | Malheur | Marion |
| Morrow | Multnomah | Polk | Sherman |
| Tillamook | Umatilla | Union | Wallowa |
| Wasco | Washington | Wheeler | Yamhill |