San Lorenzo is a census-designated place located in the East Bay of the San Francisco Bay Area in Alameda County, California, United States. The population was 29,581 at the 2020 census. It is an unincorporated community, located at the banks of San Lorenzo Creek. It was originally named Squattersville in 1851, but later renamed to San Lorenzo. In 1944, under contract to the U.S. Navy, The David D. Bohannon Company began construction of San Lorenzo Village, which was one of the nation's first planned communities, with parcels designated for schools, churches, parks, and several retail centers.