There are 36 counties in the U.S. State of Oregon. The Oregon Constitution does not explicitly provide for county seats; Article VI, covering the "Administrative Department" of the state of Oregon, simply states that:

All county and city officers shall keep their respective offices at such places therein, and perform such duties, as may be prescribed by law.^[2]

More details on the etymologies of Oregon county names and place names in general are documented in Oregon Geographic Names. Oregon's postal abbreviation is OR and its FIPS state code is 41.

The Federal Information Processing Standard (FIPS) code, which is used by the United States government to uniquely identify counties, is provided with each entry. The FIPS code for each county links to census data for that county.

More information County, FIPS code ...

County	FIPS code[3]	County seat[4]	Est.[4]	Origin[5]	Etymology[5]	Population[6]	Area[4]	Map
Baker County	001	Baker City	1862	Eastern portion of Wasco County	Named in honor of Edward Dickinson Baker (1811-1861), a senator from Oregon who was killed at Ball's Bluff, a battle of the American Civil War.	16,912	3,068 sq mi (7,946 km2)
Benton County	003	Corvallis	1847	Polk County	Named in honor of Thomas Hart Benton (1782–1858), a U.S. senator who advocated U.S. control over the Oregon Country.	97,713	676 sq mi (1,751 km2)
Clackamas County	005	Oregon City	1843	One of the original four districts of the Oregon Country	Named in honor of the Clackamas Indians, a Native American tribe living in the area.	423,173	1,868 sq mi (4,838 km2)
Clatsop County	007	Astoria	1844	Northern and western portions of the original Twality District	Named in honor of the Clatsop tribe of Native Americans, who lived along the coast of the Pacific Ocean prior to European settlement.	41,102	827 sq mi (2,142 km2)
Columbia County	009	Saint Helens	1854	Northern half of Washington County	Named for the Columbia River, which forms the county's northern borders.	53,880	657 sq mi (1,702 km2)
Coos County	011	Coquille	1853	Western parts of Umpqua and Jackson Counties	Named in honor of the Coos Tribe of Native Americans who lived in the region.	64,212	1,600 sq mi (4,144 km2)
Crook County	013	Prineville	1882	Southern part of Wasco County	Named in honor of George Crook (1828–1890), a U.S. Army officer who served in the American Civil War and the Indian Wars.	26,952	2,980 sq mi (7,718 km2)
Curry County	015	Gold Beach	1855	Coos County	Named in honor of George Law Curry (1820–1878), a governor of the Oregon Territory.	23,296	1,627 sq mi (4,214 km2)
Deschutes County	017	Bend	1916	Southern part of Crook County	Named for the Deschutes River, derived from "Riviere des Chutes", French for "River of the Falls".	208,513	3,018 sq mi (7,817 km2)
Douglas County	019	Roseburg	1852	Portion of Umpqua County which lay east of the Coast Range summit	Named in honor of Stephen A. Douglas (1813–1861), a U.S. Senator who supported Oregon statehood.	112,435	5,037 sq mi (13,046 km2)
Gilliam County	021	Condon	1885	Eastern third of Wasco County	Named in honor of Cornelius Gilliam (1798–1848), a pioneer who commanded the forces of the Provisional Government of Oregon after the Whitman massacre.	2,026	1,204 sq mi (3,118 km2)
Grant County	023	Canyon City	1864	Parts of old Wasco and old Umatilla counties	Named in honor of Ulysses S. Grant (1822–1885), army officer who served in the Oregon Territory; a Union general in the American Civil War at the time of the county's creation; and subsequently President of the United States (1869–1877).	7,215	4,529 sq mi (11,730 km2)
Harney County	025	Burns	1889	Southern two-thirds of Grant County	Named in honor of William S. Harney (1800–1889), a cavalry officer of the period, who was involved in the Pig War.	7,440	10,135 sq mi (26,250 km2)
Hood River County	027	Hood River	1908	Northwest portion of Wasco County	Named for the Hood River (a tributary of the Columbia River), which flows through the county.	23,745	522 sq mi (1,352 km2)
Jackson County	029	Medford	1852	Southwestern portion of Lane County and unorganized area south of Douglas and Umpqua Counties.	Named in honor of Andrew Jackson (1767-1845), the seventh President of the United States.	220,768	2,785 sq mi (7,213 km2)
Jefferson County	031	Madras	1914	Crook County	Named for Mount Jefferson, located on its western boundary, which was named for Thomas Jefferson.	25,454	1,781 sq mi (4,613 km2)
Josephine County	033	Grants Pass	1856	Western half of Jackson County	Named in honor of Virginia "Josephine" Rollins (1834–1912), the first white woman to make this county her home.	87,821	1,640 sq mi (4,248 km2)
Klamath County	035	Klamath Falls	1882	Western part of Lake County	Named in honor of the Klamath or Clamitte tribe, which has had a presence in the area for 10,000 years.	70,003	5,945 sq mi (15,397 km2)
Lake County	037	Lakeview	1874	Jackson and Wasco Counties	Named for numerous lakes and hot springs.	8,293	7,940 sq mi (20,565 km2)
Lane County	039	Eugene	1851	Southern part of Linn County and the portion of Benton County east of Umpqua County	Named in honor of Gen. Joseph Lane (1801–1881), the first governor of Oregon Territory.	381,181	4,554 sq mi (11,795 km2)
Lincoln County	041	Newport	1893	Western portion of Benton County and Polk County	Named in honor of Abraham Lincoln (1809-1865), the sixteenth President of the United States.	50,821	980 sq mi (2,538 km2)
Linn County	043	Albany	1847	Southern portion of Champoeg (later Marion) County	Named in honor of U.S. Senator Lewis F. Linn (1795–1843) of Missouri, author of the Donation Land Act, which provided free land to settlers in the West.	131,496	2,291 sq mi (5,934 km2)
Malheur County	045	Vale	1887	Southern portion of Baker County	Named for the Malheur River (formally "Riviere au Malheur" or "Unfortunate River"), named by French trappers whose property and furs were stolen from their river encampment.	32,044	9,888 sq mi (25,610 km2)
Marion County	047	Salem	1843	One of the original four districts of the Oregon territory	Named in honor of Francis Marion (1732-1795), a Revolutionary War general of the Continental Army from South Carolina.	346,741	1,185 sq mi (3,069 km2)
Morrow County	049	Heppner	1885	Western portion of Umatilla County and a small portion of eastern Wasco County	Named in honor of Jackson L. Morrow (1827-1899), a state representative who advocated for the formation of the county.	12,302	2,033 sq mi (5,265 km2)
Multnomah County	051	Portland	1854	Eastern part of Washington and the northern part of Clackamas counties	Named for the Native American village of Multnomah, on Sauvie Island. The word is derived from nematlnomaq, probably meaning downriver. Lewis and Clark made note of the name in 1805, and applied that name to all local Indians.	789,698	435 sq mi (1,127 km2)
Polk County	053	Dallas	1845	Yamhill District	Named in honor of James Knox Polk (1795–1849), President of the United States at the time of the county's creation	89,805	741 sq mi (1,919 km2)
Sherman County	055	Moro	1889	Northeast corner of Wasco County	Named in honor of William Tecumseh Sherman (1820–1891), American Civil War general, and businessman, educator, and author	1,951	823 sq mi (2,132 km2)
Tillamook County	057	Tillamook	1853	Clatsop, Yamhill and Polk Counties	Named in honor of the Tillamook (or Killamook) Native American people.	27,417	1,102 sq mi (2,854 km2)
Umatilla County	059	Pendleton	1862	Central portion of Wasco County	Named for the Umatilla River, derived from the Sahaptin word, possibly meaning laughing waters.	80,053	3,215 sq mi (8,327 km2)
Union County	061	La Grande	1864	Baker County	Named for the town of Union, which had been established two years before and named by its founders for the "Union" of the states during the Civil War.	25,944	2,037 sq mi (5,276 km2)
Wallowa County	063	Enterprise	1887	Eastern portion of Union County.	Named for the Nez Perce word wallowa to designate a tripod of poles used to support fish nets. The area was claimed by the Chief Joseph band of the Nez Perce as its hunting and fishing grounds.	7,674	3,145 sq mi (8,146 km2)
Wasco County	065	The Dalles	1854	Parts of Clackamas, Lane, Linn and Marion counties	Named in honor of the Wasco (or Wascopam) Native American tribe.	26,333	2,381 sq mi (6,167 km2)
Washington County	067	Hillsboro	1843	One of the original four districts of the Oregon Country (as Twality District)	Named in honor of George Washington (1732-1799), the first President of the United States.	598,865	724 sq mi (1,875 km2)
Wheeler County	069	Fossil	1899	Grant County, Gilliam County, and Crook County	Named in honor of Henry H. Wheeler (1826-1915), who operated the first mail stage line from The Dalles to Canyon City.	1,436	1,715 sq mi (4,442 km2)
Yamhill County	071	McMinnville	1843	One of the original four districts of the Oregon Country	Named in honor of the Yamhelas, members of the Kalapuya Native American family, who lived along the Yamhill River in the western Willamette Valley.	108,644	716 sq mi (1,854 km2)

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