Tuolumne County is a county in the U.S. state of California. The county seat and only incorporated city is Sonora. Tuolumne County comprises the Sonora, CA Micropolitan Statistical Area. The county is in the Sierra Nevada region. Tuolumne County borders Calaveras County to the north, Alpine County to the northeast, Mono County to the east, Mariposa County to the south, and Stanislaus County to the west.
The northern half of Yosemite National Park is located in the eastern part of the county.