Kuna is a city in Ada County, Idaho. It is part of the Boise metropolitan area. The population was 24,011 at the time of the 2020 census. Kun…Kuna is a city in Ada County, Idaho. It is part of the Boise metropolitan area. The population was 24,011 at the time of the 2020 census. Kuna is one of the fastest-growing areas in Idaho, having nearly tripled in population between 2000 and 2010 and a nearly additional 60 percent gain between 2010 and 2020.