Boise County is a rural mountain county in the U.S. state of Idaho.As of the 2020 United States Census, the population was 7,610. [1] The county seat is historic Idaho City, [2] which is connected through a series of paved and unpaved roads to Lowman, Centerville, Placerville, Pioneerville, Star Ranch, Crouch, Garden Valley, and Horseshoe Bend.