Ada County (1864 - Present)
Adams County (1911 - Present)
Alta County (1891 - 1891)
Bannock County (1893 - Present)
Bear Lake County (1875 - Present)
Benewah County (1915 - Present)
Bingham County (1885 - Present)
Blaine County (1895 - Present)
Boise County (1863 - Present)
Bonner County (1907 - Present)
Bonneville County (1911 - Present)
Boundary County (1915 - Present)
Butte County (1917 - Present)
Camas County (1917 - Present)
Canyon County (1892 - Present)
Caribou County (1919 - Present)
Cassia County (1879 - Present)
Clark County (1919 - Present)
Clark County Proposed (1905 - 1905)
Clearwater County (1911 - Present)
Clearwater County Proposed (1901 - 1901)
Custer County (1881 - Present)
Elmore County (1889 - Present)
Franklin County (1913 - Present)
Fremont County (1893 - Present)
Gem County (1915 - Present)
Gooding County (1913 - Present)
Idaho County (1861 - Present)
Jefferson County (1913 - Present)
Jerome County (1919 - Present)
Kootenai County (1864 - Present)
Latah County (1888 - Present)
Lemhi County (1869 - Present)
Lewis County (1911 - Present)
Lewis County Proposed (1905 - 1905)
Lincoln County (1891 - 1891)
Lincoln County (1895 - Present)
Logan County (1889 - 1895)
Madison County (1913 - Present)
Minidoka County (1913 - Present)
Nez Perce County (1861 - Present)
Oneida County (1864 - Present)
Owyhee County (1863 - Present)
Payette County (1917 - Present)
Power County (1913 - Present)
Selway County Proposed (1917 - 1917)
Shoshone County (1861 - Present)
Teton County (1915 - Present)
Twin Falls County (1907 - Present)
Valley County (1918 - Present)
Washington County (1879 - Present)