Counties of Idaho
Ada Adams Ban- nock Bear Lake Bene- wah Bingham Blaine Boise Bonner Bonneville Boundary Butte Camas Can- yon Caribou Cassia Clark Clearwater Custer Elmore Frank- lin Fremont Gem Good- ing Idaho Jeffer- son Jerome Koote- nai Latah Lemhi Lewis Lincoln Madi- son Mini- doka Nez Perce Oneida Owyhee Pay- ette Power Shoshone Te- ton Twin Falls Valley Wash- ington
Location	State of Idaho
Number	44
Populations	806 (Clark) – 518,907 (Ada)
Areas	408 square miles (1,060 km2) (Payette) – 8,485 square miles (21,980 km2) (Idaho)
Government	County government
Subdivisions	cities, towns, townships, unincorporated communities, Indian reservations, census designated place

There are 44 counties in the U.S. state of Idaho.

The Idaho Territory was organized in March 1863, and Owyhee County was the first county in the territory to be organized, in December of that year. Oneida County was organized in January 1864, while Missoula County was adopted the same month, before becoming part of the new Montana Territory in May. Shoshone, Nez Perce, Idaho and Boise Counties were recognized in February 1864; Alturas County was organized the same month. In December 1864, Kootenai and Ada Counties were created; Lah-Toh County was also created at this time but was abolished in 1867.

Idaho's present-day boundaries were established in 1868, and Lemhi County was created the following year. By the time Idaho was admitted to the Union as the 43rd state in 1890, a further eight counties had been created, bringing the total to 18. After Canyon, Fremont and Bannock Counties had been created, Alturas and Logan Counties were merged to form Blaine County in March 1895; Lincoln County was formed out of Blaine County later the same month. Bonner and Twin Falls Counties were created in 1907, before a further 21 counties were created between 1911 and 1919, bringing the total to the present-day 44.

Since 1945, each county has used a code on its license plates that features the first letter of the county's name. Where the names of two or more counties start with the same letter, in each of these counties the letter is preceded by a number indicating that county's order in the alphabetical list. For instance, the four counties beginning with 'L' in alphabetical order are Latah, Lemhi, Lewis and Lincoln; the codes for these counties are thus 1L, 2L, 3L and 4L respectively. Elmore, Idaho, Kootenai, Nez Perce, Shoshone, Valley, and Washington Counties are the only ones in the state with their respective first letters; in these counties, the letter alone serves as the code.

Alphabetical list

County	FIPS code[1]	County seat[2]	Est.[2]	Origin[3]	License plate prefix[4]	Etymology [5]	Population[6]	Area[2]	Map
Ada County	001	Boise	1864	Boise County	1A	Ada Riggs (1856-1909), daughter of H. C. Riggs, a member of the Idaho Territorial Legislature.	518,907	1,055 sq mi (2,732 km2)
Adams County	003	Council	1911	Washington County	2A	John Adams (1735–1826), second President of the United States (1797–1801).	4,817	1,365 sq mi (3,535 km2)
Bannock County	005	Pocatello	1893	Bingham County	1B	Bannock Native American tribe.	89,517	1,113 sq mi (2,883 km2)
Bear Lake County	007	Paris	1875	Oneida County	2B	Bear Lake on the Utah/Idaho border.	6,722	971 sq mi (2,515 km2)
Benewah County	009	St. Maries	1915	Kootenai County	3B	Ben'wah, chief of the Coeur d'Alene Tribe	10,370	776 sq mi (2,010 km2)
Bingham County	011	Blackfoot	1885	Oneida County	4B	Henry H. Bingham (1841-1912), a general in the American Civil War and a U.S. Congressman from Pennsylvania.	49,923	2,095 sq mi (5,426 km2)
Blaine County	013	Hailey	1895	Alturas and Logan Counties	5B	James G. Blaine (1830-1893), United States Secretary of State (1881, 1889-1892).	24,866	2,645 sq mi (6,851 km2)
Boise County	015	Idaho City	1864	original county	6B	Boise River	8,333	1,902 sq mi (4,926 km2)
Bonner County	017	Sandpoint	1907	Kootenai County	7B	Edwin L. Bonner (1834-1902), originator of an 1864 ferry service on the Kootenai River.	51,414	1,738 sq mi (4,501 km2)
Bonneville County	019	Idaho Falls	1911	Bingham County	8B	Benjamin Bonneville (1796-1878), a French-born explorer of the West.	129,496	1,869 sq mi (4,841 km2)
Boundary County	021	Bonners Ferry	1915	Bonner County	9B	Borders Canada on the north.	13,345	1,269 sq mi (3,287 km2)
Butte County	023	Arco	1917	Bingham, Blaine, and Jefferson Counties	10B	Buttes rising from the Snake River Plain.	2,684	2,233 sq mi (5,783 km2)
Camas County	025	Fairfield	1917	Blaine County	1C	Camassia, a plant species important as a food source among Native Americans and early settlers.	1,153	1,077 sq mi (2,789 km2)
Canyon County	027	Caldwell	1892	Ada County	2C	Disputed, either a canyon of the Boise River near Caldwell or a canyon of the Snake River which forms part of the county's boundary.	251,065	590 sq mi (1,528 km2)
Caribou County	029	Soda Springs	1919	Bannock County	3C	Caribou Mountains	7,190	1,766 sq mi (4,574 km2)
Cassia County	031	Burley	1879	Owyhee County	4C	Disputed, either Cassia Creek or a member of the Mormon Battalion, James John Cazier (1821-1890).	25,655	2,567 sq mi (6,648 km2)
Clark County	033	Dubois	1919	Fremont County	5C	Sam K. Clark (1857-1933), early settler and a member of the Idaho Senate.	806	1,765 sq mi (4,571 km2)
Clearwater County	035	Orofino	1911	Nez Perce County	6C	Clearwater River	9,015	2,462 sq mi (6,377 km2)
Custer County	037	Challis	1881	Alturas and Lemhi Counties	7C	General Custer mine, named after George Armstrong Custer (1839-1876), United States Army general.	4,506	4,926 sq mi (12,758 km2)
Elmore County	039	Mountain Home	1889	Alturas County	E	Ida Elmore mines, locally noted for gold and silver production in the 1860s.	29,403	3,078 sq mi (7,972 km2)
Franklin County	041	Preston	1913	Oneida County	1F	Franklin D. Richards (1821-1899), early LDS Church apostle.	15,189	666 sq mi (1,725 km2)
Fremont County	043	Saint Anthony	1893	Bingham County	2F	John C. Frémont (1813-1890), an explorer of the West.	13,978	1,867 sq mi (4,836 km2)
Gem County	045	Emmett	1915	Boise and Canyon Counties	1G	State nickname of "Gem State."	20,418	563 sq mi (1,458 km2)
Gooding County	047	Gooding	1913	Lincoln County	2G	Frank R. Gooding (1859-1928), seventh Governor of Idaho (1905-1909), U.S. Senator (1921-1928).	15,715	731 sq mi (1,893 km2)
Idaho County	049	Grangeville	1864	original county	I	Columbia River steamship Idaho launched in 1860. Name predates both Idaho Territory and the State of Idaho.	17,593	8,485 sq mi (21,976 km2)
Jefferson County	051	Rigby	1913	Fremont County	1J	Thomas Jefferson (1743-1826), third President of the United States (1801-1809).	33,428	1,095 sq mi (2,836 km2)
Jerome County	053	Jerome	1919	Gooding and Lincoln Counties	2J	Disputed, either North Side Irrigation Project developer Jerome Hill, his son-in-law Jerome Kuhn (1898-1952), or his grandson Jerome Kuhn, Jr.	25,311	600 sq mi (1,554 km2)
Kootenai County	055	Coeur d'Alene	1864	Nez Perce County	K	Kootenai Native American tribe.	183,578	1,245 sq mi (3,225 km2)
Latah County	057	Moscow	1888	Nez Perce County	1L	Latah Creek, Nez Perce for "the place of pine trees and sestle."	40,978	1,077 sq mi (2,789 km2)
Lemhi County	059	Salmon	1869	Idaho County	2L	Limhi, king of the Nephites according to the Book of Mormon.	8,240	4,564 sq mi (11,821 km2)
Lewis County	061	Nezperce	1911	Nez Perce County	3L	Meriwether Lewis (1774-1809), a leader of the Lewis and Clark Expedition.	3,763	479 sq mi (1,241 km2)
Lincoln County	063	Shoshone	1895	Blaine County	4L	Abraham Lincoln (1809-1865), sixteenth President of the United States (1861-1865). Idaho Territory was founded under Lincoln's administration.	5,329	1,206 sq mi (3,124 km2)
Madison County	065	Rexburg	1913	Fremont County	1M	James Madison (1751-1836), fourth President of the United States (1809-1817).	54,976	472 sq mi (1,222 km2)
Minidoka County	067	Rupert	1913	Lincoln County	2M	Disputed Native American origin, either Lakota for "a fountain or spring of water" or Shoshoni for "broad expanse."	22,194	760 sq mi (1,968 km2)
Nez Perce County	069	Lewiston	1864	original county	N	The Nez Perce, a Native American tribe.	43,004	849 sq mi (2,199 km2)
Oneida County	071	Malad City	1864	original county	1O	Oneida Lake in New York state, where many early settlers were from.	4,712	1,200 sq mi (3,108 km2)
Owyhee County	073	Murphy	1863	original county	2O	Alternate spelling of Hawaii. Hawaiian fur trappers explored the area in 1819 and 1820.	12,613	7,678 sq mi (19,886 km2)
Payette County	075	Payette	1917	Canyon County	1P	Francois Payette (1793-1844?), Canadian-born fur trader and early settler.	26,956	408 sq mi (1,057 km2)
Power County	077	American Falls	1913	Bingham, Blaine, and Oneida Counties	2P	The American Falls Power Plant	8,068	1,406 sq mi (3,642 km2)
Shoshone County	079	Wallace	1864	original county	S	Shoshone Native American tribe.	14,012	2,634 sq mi (6,822 km2)
Teton County	081	Driggs	1915	Bingham, Fremont, and Madison Counties	1T	Teton Range in Wyoming.	12,544	450 sq mi (1,165 km2)
Twin Falls County	083	Twin Falls	1907	Cassia County	2T	Twin Falls waterfall on the Snake River.	93,696	1,925 sq mi (4,986 km2)
Valley County	085	Cascade	1917	Boise and Idaho Counties	V	Long Valley located in the county.	12,464	3,733 sq mi (9,668 km2)
Washington County	087	Weiser	1879	Ada County	W	George Washington (1732-1799), first President of the United States (1789-1797).	11,087	1,456 sq mi (3,771 km2)

Extinct counties

• Alturas County created February 4, 1864, and abolished March 5, 1895.
• Logan County created February 7, 1889, and abolished March 5, 1895.