Alum Rock (/ˈæləm/) is a census-designated place (CDP) in Santa Clara County, California, United States and a community of San Jose. The CDP, which excludes all annexed areas, had a population of 15,536 at the 2010 census. Alum Rock was named after a rock formerly thought to be composed of alum in nearby Alum Rock Park. Formerly a separate town, much of the community is unincorporated surrounded by incorporated San Jose; neighborhoods between White Road and Capitol Avenue are part of a city/county agreement for annexation. James Lick High School, Mt. Pleasant High School, and William C. Overfelt High School (which are part of the East Side Union High School District), Joseph George Middle School, Ocala Middle School, and other schools in the Alum Rock Union School District serve the neighborhood.