Mount Baldy or Mt Baldy, formerly Camp Baynham and Camp Baldy, is an unincorporated community in the San Gabriel Mountains, in San Bernardino County near the eastern border of Los Angeles County, in southern California.
It is located below Mount San Antonio (Mt Baldy) in San Antonio Canyon. San Antonio Creek flows through the community. It is surrounded by Angeles National Forest. Mt Baldy is 12 miles (19 km) north of Ontario.
Mt Baldy has a post office with ZIP code 91759.The community was established as Camp Baynham in 1906; it changed its name to Camp Baldy in 1910 and became Mt Baldy in 1951. Its post office was established in 1913.