Description Magical Adventures, Clear Creek, Boise River Greenbelt, ID, Ada CountyIn The Wild Near By, Clear Creek, Eagle, IDAda County is located in the southwestern part of the U.S. state of Idaho. As of the 2020 United States Census, the county had a population of 494,967, making it the state's most populous county, with 26.8% of the state's 2020 population. The county seat and largest city is Boise, which is also the state capital. Wikipedia