History Castilleja was founded in 1907 by Mary Ishbel Lockey. Originally from Montana, Lockey graduated from Stanford University in 1902, majoring in English. Lockey was a charter member of Alpha Phi and was the first Stanford Alpha Phi elected to Phi Beta Kappa. She was encouraged by Stanford's first president, David Starr Jordan, to start a school that would offer girls a comprehensive, college preparatory education. In its early years, some boys were allowed to take classes at Castilleja.

The school's core values, known as "the 5 Cs," include conscience, courtesy, character, courage, and charity. In 1926, the Castilleja chapel was designed by architect Birge Clark, in a complimentary design to the existing administration building. One concern has been traffic impact. In June 2022, the

Amy Chow, Olympic gold medalist in gymnastics, pediatrician Beatrice Judd Ryan, art dealer, curator Grace Slick, singer and songwriter Helen Katharine Forbes, 1908 graduate, muralist and painter Josie Maran, actress and model Nancy Ditz, Olympic marathon runner Pansy Ho, Macau-born heiress and operator of casinos Penny Pritzker, philanthropist; U.S. Secretary of Commerce and member of the Pritzker family. Tori Anthony, pole vaulter