 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.According to the U.S. Census Bureau, the county has a total area of , of which is land and (2.7%) is water.At the 2000 census, there were 131,441 people, 45,018 households and 33,943 families living in the county.