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Revised 27 December 2010


Idaho was the last state to be created from the Oregon Territory.  At the time of its formation as a Territory, on 3 March 1853, it included all of Montana and nearly all of Wyoming.  Montana became a territory in its own right in 1864 and Wyoming was created in 1868.  The six original counties were formed between the years 1861 and 1865.  

The southern portion of Idaho, which borders Utah, was the first section to be settled.  A group of Mormon emigrants from northern Europe established permanent settlements in that region were the first known to do so.

In 1860, a mining boom attracted people from the East and Mid-West to the Idaho valleys.  The construction of large irrigation systems and districts around the Snake River, which winds its way throughout this area, drew many western and Midwestern farm families to the area around 1910 to farm the newly irrigated lands.

Although Catholic and Protestant churches are represented in most of the Idaho communities, the predominant religion in the area are those who follow the teachings of the Church of Jesus Christ of Latter-day Saints. (aka Mormons).


Name Date Formed Parent County County Seat
Ada 1864 Boise Boise
Adams 1911 Washington Council
Alturas Original County.  It was discontinued in 1895, becoming part of Lincoln and Blaine Counties.
Bannock 1893 Oneida, Bear Lake Pocatello
Bear Lake 1875 Oneida Paris
Benewah 1915 Kootenai St. Maries
Bingham 1885 Oneida Blackfoot
Blaine 1895 Alturas Hailey
Boise 1863 Original County Idaho City
Bonner 1907 Kootenai Sandpoint
Bonneville 1911 Bingham Idaho Falls
Boundary 1915 Bonner Bonner's Ferry
Butte 1917 Bingham, Blaine, Jefferson Arco
Camas 1917 Blaine Fairfield
Canyon 1892 Owyhee, Ada Caldwell
Caribou 1919 Bannock, Oneida Soda Springs
Cassia 1879 Oneida Burley
Clark 1919 Fremont DuBois
Clearwater 1911 Nez Perce Orofino
Custer 1881 Alturas Challis
Elmore 1889 Alturas, Ada Mountain Home
Franklin 1913 Oneida Preston
Freemont 1893 Gingham, Lemnhi St. Anthony
Gem 1915 Boise, Canyon Emmett
Gooding 1913 Lincoln Gooding
Idaho 1862 Original County Grangeville
Jefferson 1913 Fremont Rigby
Jerome 1919 Gooding, Lincoln Jerome
Kootenai 1864 Nez Perce Coeur d'Alene
Latah (Created and organized by U.S. Congressional enactment & said to be the only county in the United States so created. 1888 Nez Perce Moscow
Lemhi 1869 Idaho Salmon
Lewis 1911 Nez Perce Nez Perce
Lincoln 1895 Alturas Shoshone
Madison 1913 Fremont Rexburg
Minidoka 1913 Lincoln Rupert
Nez Perce 1861 Original County Lewiston
Oneida 1865 Original County Malad City
Owyhee 1863 Original County Murphy
Payette 1917 Canyon Payette
Power 1913 Bingham, Blaine, Oneida American Falls
Shoshone 1861 Original County Wallace
Teton 1915 Madison, Fremont Driggs
Twin Falls 1907 Cassia Twin Falls
Valley 1917 Boise, Idaho Cascade
Washington 1879 Boise Weiser
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Idaho GenWeb Idaho State Historical Society Home Page
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Special Collections Black History Museum
Idaho Mining Association - History Idaho Historical Museum
Idaho - The States - The History Channel Idaho Genealogy Search
Native Americans in Idaho Idaho History Timeline
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