| County | FIPS Code | County Seat | Established in | Population | Area (sq mi) | Area (km2) |
|---|---|---|---|---|---|---|
| Baker County | 1 | Baker City | 1862 | 16,510 | 3,068 | 7,946 |
| Benton County | 3 | Corvallis | 1847 | 91,320 | 676 | 1,751 |
| Clackamas County | 5 | Oregon City | 1843 | 404,980 | 1,868 | 4,838 |
| Clatsop County | 7 | Astoria | 1844 | 38,225 | 827 | 2,142 |
| Columbia County | 9 | Saint Helens | 1854 | 50,795 | 657 | 1,702 |
| Coos County | 11 | Coquille | 1853 | 63,190 | 1,600 | 4,144 |
| Crook County | 13 | Prineville | 1882 | 21,580 | 2,980 | 7,718 |
| Curry County | 15 | Gold Beach | 1855 | 22,600 | 1,627 | 4,214 |
| Deschutes County | 17 | Bend | 1916 | 176,635 | 3,018 | 7,817 |
| Douglas County | 19 | Roseburg | 1852 | 110,395 | 5,037 | 13,046 |
| Gilliam County | 21 | Condon | 1885 | 1,980 | 1,204 | 3,118 |
| Grant County | 23 | Canyon City | 1864 | 7,410 | 4,529 | 11,730 |
| Harney County | 25 | Burns | 1889 | 7,320 | 10,135 | 26,250 |
| Hood River County | 27 | Hood River | 1908 | 24,735 | 522 | 1,352 |
| Jackson County | 29 | Medford | 1852 | 213,765 | 2,785 | 7,213 |
| Jefferson County | 31 | Madras | 1914 | 22,790 | 1,781 | 4,613 |
| Josephine County | 33 | Grants Pass | 1856 | 84,675 | 1,640 | 4,248 |
| Klamath County | 35 | Klamath Falls | 1882 | 67,410 | 5,945 | 15,397 |
| Lake County | 37 | Lakeview | 1874 | 8,015 | 7,940 | 20,565 |
| Lane County | 39 | Eugene | 1851 | 365,940 | 4,554 | 11,795 |
| Lincoln County | 41 | Newport | 1893 | 47,735 | 980 | 2,538 |
| Linn County | 43 | Albany | 1847 | 122,315 | 2,291 | 5,934 |
| Malheur County | 45 | Vale | 1887 | 31,705 | 9,888 | 25,610 |
| Marion County | 47 | Salem | 1843 | 333,950 | 1,185 | 3,069 |
| Morrow County | 49 | Heppner | 1885 | 11,745 | 2,033 | 5,265 |
| Multnomah County | 51 | Portland | 1854 | 790,670 | 435 | 1,127 |
| Polk County | 53 | Dallas | 1845 | 79,730 | 741 | 1,919 |
| Sherman County | 55 | Moro | 1889 | 1,795 | 823 | 2,132 |
| Tillamook County | 57 | Tillamook | 1853 | 25,920 | 1,102 | 2,854 |
| Umatilla County | 59 | Pendleton | 1862 | 79,880 | 3,215 | 8,327 |
| Union County | 61 | La Grande | 1864 | 26,745 | 2,037 | 5,276 |
| Wallowa County | 63 | Enterprise | 1887 | 7,140 | 3,145 | 8,146 |
| Wasco County | 65 | The Dalles | 1854 | 26,700 | 2,381 | 6,167 |
| Washington County | 67 | Hillsboro | 1843 | 583,595 | 724 | 1,875 |
| Wheeler County | 69 | Fossil | 1899 | 1,465 | 1,715 | 4,442 |
| Yamhill County | 71 | McMinnville | 1843 | 104,990 | 716 | 1,854 |
