Mono County /ˈmoʊnoʊ/(MOH-noh) is a county in the U.S. state of California. As of the 2020 census, the population was 13,195,[1] making it the fourth-least populous county in California. The county seat is Bridgeport.[2][3] The county is located east of the Sierra Nevada between Yosemite National Park and Nevada. Mono County was founded in 1861.