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History and Facts of Idaho Counties

Today’s Idaho counties did not always exist in the present form. They went through many different changes in the space of a few short years.

Idaho Territory Counties

The Idaho Territory was organized on March 3, 1863 from the Washington Territory, and lasted until July 3, 1890, when the final extent of the territory was admitted to the Union as Idaho.

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 with Alturas County organizing later the same month.

In December 1864, Kootenai and Ada Counties were created and 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.

The State of Idaho entered the union as the 43rd state on July 3, 1890 with a total of 18 counties.

Idaho Counties Today

Today, Idaho is divided into 44 counties. States bordering Idaho are MontanaNevadaOregonUtahWashingtonWyoming and Canada.

Each county serves as the local level of government within its borders.

Fun Facts about Idaho Counties

Counties by Year

County Size Facts

County Population Facts

  • Clark County (982) is the least populated county in Idaho.
  • Ada County (392,365) is the most populated county in Idaho.

Idaho City Facts

Idaho’s 10  largest cities (2017 est.) are:

  1. Boise (226,570) is in Ada County
  2. Meridian (99,926) is in Ada County
  3. Nampa (93,590) is in Canyon County
  4. Idaho Falls (61,076) is in Bonneville County
  5. Pocatello (55,193) is in Bannock County
  6. Caldwell (54,660) is in Canyon County
  7. Coeur d’Alene (50,665) is in Kootenai County
  8. Twin Falls (49,202) is in Twin Falls County
  9. Post Falls (33,290) is in Kootenai County
  10. Lewiston (32,820) is in Nez Perce County

Boundary Changes of Idaho Counties from 1816 to 1872

This Interactive Map of Idaho Counties  show the historical boundaries, names, organization, and attachments of every county, extinct county and unsuccessful county proposal from the creation of Idaho in 1848-1965.

List of Idaho Counties

List of Old Former / Extinct Idaho Counties

There are some Idaho counties that no longer exist because they were discontinued, renamed or merged with another county. These are important for genealogy research purposes.

The below Idaho counties no longer exist:

Alta County, Idaho

Created on March 3, 1891 from Alturas, Boise and Logan counties. On May 36, 1891, the Idaho Supreme Court declared the act creating Alta County unconstitutional because it failed to provide for an election.

All territory to Alturas, Boise and Logan counties and  Alta County was abolished. 

Alturas County, Idaho Territory

Alturas County was created by the Idaho Territorial Legislature on February 4, 1864 from Boise County with the mining camp of Rocky Bar designated as the county seat.

The county was name comes from a Spanish word for “mountain summits” or “mountainous heights.” The county seat was moved to Hailey in 1882.

It covered an area larger than the states of Maryland, New Jersey, and Delaware combined. Most present-day southern Idaho counties were created at least in part from the original Alturas County area.

In 1889, the Idaho Territorial Legislature created Elmore County and Logan County from parts of Alturas County.

On March 3, 1891, Alturas County was used to create Alta County.

On May 6, 1891  Alturas County was restored, with slightly different boundaries, when the Idaho Supreme Court declared the act creating Alta County and Lincoln County unconstitutional because it failed to provide for an election. 

On March 5, 1895, to go around a recent state supreme court decision striking down an earlier county reorganization, the Idaho Legislature combined Alturas and Logan Counties into a new county called Blaine County

Two weeks later on March 18, 1895, the southern portion of the newly-created Blaine County was split off to form Lincoln County with its county seat at Shoshone. Hailey remained the county seat of what was now Blaine County and Alturas County disappeared from the Idaho map.

Beaverhead County, Idaho Territory

Beaverhead County was created by the Idaho Territorial Legislature on January 16, 1864 from unorganized land areas, with the county seat at Bannock City.

Beaverhead County became a Montana Territory county on May 26, 1864.

Big Horn County, Idaho Territory

Big Horn County was created by the Idaho Territorial Legislature on January 16, 1864 from unorganized land areas, county seat to be located by commissioners.

Big Horn County became a Montana Territory county on May 26, 1864.

Choteau County, Idaho Territory

Choteau County was created by the Idaho Territorial Legislature on January 16, 1864 from unorganized land areas, with the county seat at Fort Benton.

Choteau County became a Montana Territory county on May 26, 1864.

Clark County, (Proposed) Idaho

Legislature authorized creation on February 28, 1905 from Kootenai County. Proposal failed on May 12, 1905 when the Idaho Supreme Court declared the act unconstitutional.

Clearwater County, (Proposed) Idaho

Legislature authorized creation on March 21, 1901 from Nez Perce and Shoshone counties. Proposal failed on June 14, 1901 when the Idaho Supreme Court declared the act invalid.

Dawson County, Idaho Territory

Dawson County was created by the Idaho Territorial Legislature on January 16, 1864 from unorganized land areas, with the
county seat at Fort Andrews.

Dawson County became a Montana Territory county on May 26, 1864.

Dear Lodge County, Idaho Territory

Dear Lodge County was created by the Idaho Territorial Legislature on January 16, 1864 from Idaho, Missoula counties and unorganized land areas, with the county seat at Idaho City (near the Cottonwood Fork of Deer Lodge River).

Dear Lodge County became a Montana Territory county on May 26, 1864.

Jefferson County, Idaho Territory

Jefferson County was created by the Idaho Territorial Legislature on January 16, 1864 from unorganized land areas, with the
county seat at Gallatin.

Jefferson County became a Montana Territory county on May 26, 1864.

Lah-Toh County, Idaho Territory

Lah-Toh County was created by the Idaho Territorial Legislature on January 16, 1864 from unorganized land areas, with Coeur d’Alene as its county seat.

Lah-Toh County was abolished on January 9, 1867, with the area absorbed by Nez Perce County and Kootenai County.

Lewis County, (Proposed) Idaho

Legislature authorized creation on February 28, 1905 from Kootenai County. Proposal failed on May 12, 1905 when the Idaho Supreme Court declared the act unconstitutional.

Lincoln County, Idaho

Created on March 3, 1891 from Logan County. On May 6, 1891, the Idaho Supreme Court declared the act creating Lincoln County unconstitutional because it failed to provide for an election.

All territory to Logan County and  Lincoln County was abolished.

Logan County, Idaho

Created on February 7, 1889 from Alturas County, with Bellevue as its county seat.

On March 3, 1891, Logan County was used to create Alta and Lincoln Counties.

On May 6, 1891  Logan County was restored when the Idaho Supreme Court declared the act creating Alta and Lincoln Counties unconstitutional because it failed to provide for an election. 

In 1895, the Idaho Legislature attempted to return Bellevue to Alturas County, but the plan was struck down by the state supreme court.

In response on March 5, 1895, the Idaho Legislature combined Alturas and Logan Counties into a new county called Blaine County.

Madison County, Idaho Territory

Madison County was created by the Idaho Territorial Legislature on January 16, 1864 from unorganized land areas, with the
county seat at Virginia City.

Madison County became a Montana Territory county on May 26, 1864.

Missoula County, Washington Territory

Missoula County was created by the Washington Territorial Legislature on December 14, 1860 from unorganized land areas, with the county seat at Wardensville; which included parts of present Idaho and Montana.

Missoula County became a became an Idaho Territory county when the United States created Idaho Territory from Dakota, Nebraska, and Washington Territories on March 3, 1863.

Missoula County became a Montana Territory county on May 26, 1864.

Ogalala County, Idaho Territory

Ogalala County was created by the Idaho Territorial Legislature on January 16, 1864 from unorganized land areas, with the
county seat at Fort Laramie. Ogalala County was located entirely in the eastern half of present Wyoming.

Ogalala County became a Dakota Territory county on May 26, 1864.

Selway County, (Proposed) Idaho

Legislature authorized creation on March 14, 1917 from Idaho and Lewis counties. It was dependent on a vote in the special election on July 2, 1917. The proposal failed in referendum.

Yellowstone County, Idaho Territory

Yellowstone County was created by the Idaho Territorial Legislature on January 16, 1864 from unorganized land areas, with the county seat to be located by commissioners.

Yellowstone County was located entirely within present day Wyoming. Yellowstone County became a Dakota Territory county on May 26, 1864.