Alum Rock is a census-designated place and neighborhood of San Jose, California. The population was 13,479 at the 2000 census. Alum Rock was named after a rock formerly thought to be composed of alum in nearby Alum Rock Park. Formerly a separate town, it is now an unincorporated community in Santa Clara County. James Lick High School, Joseph George Middle School and other schools in the Alum Rock Union School District serve the neighborhood. Alum Rock apartments for rent comparison page shows most up to date rent information on Alum Rock apartments and houses. Rent information is obtained from multiple rental sources but we cannot guarantee their accuracy.