county, northwestern Nevada, U.S., bordering Washoe county on the west and the state of Oregon on the north. The county consists mostly of mountains (including the Black Rock, Santa Rosa, and Jackson ranges) and desert (including a large portion of Black Rock Desert in the southwest); a large segment of Humboldt National Forest is in the northeast.

Winnemuca (Winnemucca), the county seat near the county's southern border, was once a supply station on the pioneer Oregon Trail and later became a station on the transcontinental railroad leading to Reno and San Francisco Bay. Humboldt, one of Nevada's original counties, was created in 1861.

The major economic activity is gold and silver mining. Area 9,648 square miles (24,989 square km). Pop. (2000) 16,106; (2007 est.) 17,523.