Humboldt County is a county located in the U.S. state of California. As of the 2020 census, the population was 136,463. The county seat is Eureka. Humboldt County comprises the Eureka–Arcata–Fortuna, California, Micropolitan Statistical Area. It is located on the far North Coast of California, about 270 miles north of San Francisco. It has among the most diverse climates of United States counties, with very mild coastal summers and hot interior days.