The state of Idaho is divided into 44 counties. Owyhee County is the oldest (formed in 1863) while Caribou County is the youngest (established in 1919).

Ada County is the most populous, with a population of 392,365 people. Idaho County has the most land area (21,976 km2), while Payette County has the smallest (1,057 km2).

Please find a list of all Idaho counties sorted alphabetically below.

• Ada County, ID
• Adams County, ID
• Bannock County, ID
• Bear Lake County, ID
• Benewah County, ID
• Bingham County, ID
• Blaine County, ID
• Boise County, ID
• Bonner County, ID
• Bonneville County, ID
• Boundary County, ID
• Butte County, ID
• Camas County, ID
• Canyon County, ID
• Caribou County, ID
• Cassia County, ID
• Clark County, ID
• Clearwater County, ID
• Custer County, ID
• Elmore County, ID
• Franklin County, ID
• Fremont County, ID
• Gem County, ID
• Gooding County, ID
• Idaho County, ID
• Jefferson County, ID
• Jerome County, ID
• Kootenai County, ID
• Latah County, ID
• Lemhi County, ID
• Lewis County, ID
• Lincoln County, ID
• Madison County, ID
• Minidoka County, ID
• Nez Perce County, ID
• Oneida County, ID
• Owyhee County, ID
• Payette County, ID
• Power County, ID
• Shoshone County, ID
• Teton County, ID
• Twin Falls County, ID
• Valley County, ID
• Washington County, ID