Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Tuolumne County is a county located in the Sierra Nevada of the U.S. state of California. The northern half of Yosemite National Park is located in the eastern part of the county. As of 2000 the population was 54,501. The county seat is Sonora, the county''s only incorporated city.Tuolumne County was one of the original counties of California, created in 1850 at the time of statehood. Prior to statehood, it had been referred to as Oro County. Parts of the county were given to Stanislaus County in 1854 and to Alpine County in 1864.