Tuolumne County is located in the Sierra Nevada of the U.S. state of California. The county seat is Sonora, the county's only incorporated city.
Tuolumne County was one of the original counties of California, created in 1850. The name Tuolumne is of Native American origin and has been given different meanings, such as Many Stone Houses, The Land of Mountain Lions and, Straight Up Steep. The county has a total area of 2,274 mi², 98% of it is land and 2% of it is water. As of 2000, there were 54,501 people, 21,004 households, and residing in the county.