| Name of County
|
Date Formed
|
Boundary Changes
|
Parent County
|
Counties Created by Boundary Changes
|
| Baker
|
1862 Sep 22
|
Details
|
Wasco
|
Malheur 1887, Union 1864
|
| Benton
|
1847 Dec 23
|
Details
|
Polk
|
Lincoln 1893, Umpqua 1851
|
| Champoeg
|
1843 Jul 05
|
Details
|
Oregon Country
|
Linn 1847, renamed Marion 1849
|
| Clackamas
|
1843 Jul 05
|
Details
|
Oregon Country
|
Multnomah 1854, Wasco 1854
|
| Clark
|
1843 Jul 05
|
Details
|
Oregon Country
|
now in Washington State
|
| Clatsop
|
1844 Jun 22
|
Details
|
Twality
|
Tillamook 1853
|
| Columbia
|
1854 Jan 16
|
Details
|
Washington
|
none
|
| Coos
|
1853 Dec 22
|
Details
|
Umpqua, Jackson
|
Curry 1855
|
| Crook
|
1882 Oct 24
|
Details
|
Wasco
|
Deschutes 1916, Jefferson 1914, Wheeler 1899
|
| Curry
|
1855 dec 18
|
Details
|
Coos
|
none
|
| Deschutes
|
1916 Dec 13
|
Details
|
Crook
|
none
|
| Douglas
|
1852 Jan 07
|
Details
|
Umpqua
|
Wasco 1854
|
| Gilliam
|
1885 Feb 25
|
Details
|
Wasco
|
Wheeler 1899
|
| Grant
|
1864 Oct 14
|
Details
|
Wasco, Umatilla
|
Harney 1889, Wheeler 1899
|
| Harney
|
889 Feb 23
|
Details
|
Grant
|
none
|
| Hood River
|
1908 Jun 23
|
Details
|
Wasco
|
none
|
| Jackson
|
1852 Jan 12
|
Details
|
Umpqua
|
Coos 1853, Josephine 1856, Lake 1874, Wasco 1854
|
| Jefferson
|
1914 Dec 12
|
Details
|
Crook
|
none
|
| Josephine
|
1856 Jan 22
|
Details
|
Jackson
|
none
|
| Klamath
|
1882 Oct 17
|
Details
|
Lake
|
none
|
| Lake
|
1874 Oct 24
|
Details
|
Jackson, Wasco
|
Klamath 1882
|
| Lane
|
1851 Jan 28
|
Details
|
Linn, Umpqua
|
Wasco 1854
|
| Lewis
|
1845 Dec 09
|
Details
|
Oregon Country
|
now in Washington State
|
| Lincoln
|
1893 Feb 20
|
Details
|
Benton, Polk
|
none
|
| Linn
|
1847 Dec 28
|
Details
|
Champoeg
|
Lane 1851, Umpqua 1851, Wasco 1854
|
| Malheur
|
1887 Feb 17
|
Details
|
Baker
|
none
|
| Marion
|
1849 Sep 03
|
Details
|
renamed from Champoeg
|
Wasco 1854
|
| Morrow
|
1885 Feb 16
|
Details
|
Umatilla
|
none
|
| Multnomah
|
1854 Dec 22
|
Details
|
Washington, Clackamas
|
none
|
| Polk
|
1845 Dec 22
|
Details
|
Yamhill
|
Benton 1847, Lincoln 1893, Tillamook 1853
|
| Sherman
|
1889 Feb 25
|
Details
|
Wasco
|
none
|
| Tillamook
|
1853 Dec 15
|
Details
|
Clatsop, Polk, Yamhill
|
none
|
| Twality
|
1843 Jul 05
|
Details
|
Oregon Country
|
renamed Washington 1845
|
| Umatilla
|
1862 Sep 27
|
Details
|
Wasco
|
Grant 1864, Morrow 1885
|
| Umpqua
|
1851 Jan 28
|
Details
|
Benton, Linn
|
Coos 1853, Douglas 1852, Jackson 1852, Lane 1851, dissolved into Douglas 1863
|
| Union
|
1864 Oct 14
|
Details
|
Baker
|
Wallowa 1887, Baker 1901
|
| Wallowa
|
1887 Feb 11
|
Details
|
Union
|
none
|
| Wasco
|
1854 Jan 11
|
Details
|
Clackamas, Marion, Linn, Lane, Douglas, Lewis County, Washington, Clark County, Washington (entire area east of Cascades)
|
Baker 1862, Crook 1882, Gilliam 1855, Grant 1864, Hood River 1908, Lake 1874, Sherman 1889, Umatilla 1862
|
| Washington
|
1845 Dec 22
|
Details
|
renamed from Twality
|
Columbia 1854, Multnomah 1854
|
| Wheeler
|
1899 Feb 17
|
Details
|
Crook, Gilliam, Grant
|
none
|
| Yamhill
|
1843 Jul 05
|
Details
|
Oregon Country
|
Polk 1845, Tillamook 1853
|