Modoc County is a county located in the far northeast corner of the U.S. state of California. Its population is 8,700 as of the 2020 census, down from 9,686 from the 2010 census. This makes it California's third-least-populous county. The county seat and only incorporated city is Alturas. Previous County seats include Lake City and Centerville. The county borders Nevada and Oregon. Much of Modoc County is federal land. From Wikipedia