Owyhee County is a county located in the southwestern corner of the U.S. state of Idaho. As of the 2010 census, the population was 11,526. The county seat is Murphy, and its largest city is Homedale. In area it is the second-largest county in Idaho, behind Idaho County.
On December 31, 1863, Owyhee County became the first county organized by the Idaho Territorial Legislature. While Boise, Idaho, Nez Perce and Shoshone counties were organized under the laws of Washington Territory, they were not recognized by the Idaho Territory until February 1864. The original county seat at Ruby City was moved to nearby Silver City in 1867.
Owyhee County's original boundary was the portion of Idaho Territory south of the Snake River and west of the Rocky Mountains. Less than a month after the creation of Owyhee County, Oneida County was formed in January 1864 from the eastern portion of the county. The formation of Cassia County in 1879 took further territory in the east. The county gained its present boundaries in 1930 after an election approved moving a portion of Owyhee County near Glenns Ferry and King Hill to neighboring Elmore County. In 1934 the county seat was moved from the nearly abandoned Silver City to its present location in Murphy.
Owyhee County's history is inextricably linked to the mining boom that dominated Idaho Territory in the second half of the 19th Century. Silver City and Ruby City are among the state's most noteworthy ghost towns from the period. At its height in the 1880s, Owyhee County was among the most populous places in Idaho. Today it is among the least populous, at 1.4 persons per square mile (0.5 per km²).