Mount Bullion is a census-designated place (CDP) in Mariposa County, California, United States, along California State Route 49 in the Mother Lode country of the western Sierra Nevada. The community lies 5 miles (8 km) northwest of Mariposa, the county seat, at an elevation of 2,152 feet (656 m). The population was 154 at the 2020 United States census.