Established February 4, 1864 with its county seat at Idaho City. Named for the Boise River, which was named by French-Canadian explorers and trappers for the great variety of trees growing along its banks. The Boise Basin, in which Idaho City lies, was one of the richest gold mining districts in the nation after the discovery of gold in 1862. At its peak in the 1860s and 1870s, Idaho City was, for a time, the largest city in the northwest, it was this great influx of people that lead to the establishment of the Idaho Territory.
County Seat: Idaho City