Modoc is a county 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. Several federal agencies, including the United States Forest Service, Bureau of Land Management, National Park Service, Bureau of Indian Affairs, and the United States Fish and Wildlife Service, have employees assigned to the area, and their operations are a significant part of its economy and services.