San Lucas is a census-designated place in Monterey County, California, United States. San Lucas was founded in 1886 and named after the San Lucas Rancho, which was granted in 1842 and named in honor of Saint Luke. The post office was first established in 1892.San Lucas is located in the Salinas Valley, on the Salinas River 8 miles southeast of King City, at an elevation of 410 feet.The population was 269 at the 2010 census, down from 419 at the 2000 census.