Canyon County is a county located in the U.S. state of Idaho. At the 2010 Census, the county had a population of 188,923. The county seat is Caldwell, and its largest city is Nampa.. Canyon County is part of the Boise City–Nampa, Idaho Metropolitan Statistical Area.
Hudson's Bay Company established Fort Boise in 1834 near what is now Parma, but abandoned it in 1855. Migrants traveled through Canyon County on the Oregon Trail. The Oregon Short Line Railroad was completed in the area in 1883.
The county was established on March 7, 1891, with its county seat at Caldwell. Partitioned from Ada County, it originally included Payette County (1917) and the southern portion of Gem County (1915). Some sources attribute the name to the canyon of the Boise River near Caldwell, while western writers John Rees and Vardis Fisher believed it was named for the Snake River canyon, which forms a natural boundary with Owyhee County to the south and west.