Elk River is a city in the northwestern United States in Clearwater County, Idaho. The population was 125 at the 2010 census, down from 156 i…Elk River is a city in the northwestern United States in Clearwater County, Idaho. The population was 125 at the 2010 census, down from 156 in 2000. It is accessed from State Highway 8 from Bovill, to the west in adjacent Latah County. Formerly the site of a Potlatch sawmill, it was phased out after several decades during the 1930s.