The Ishikawa of Mikawa province claimed descent from Minamoto Yoshiie (1039-1106). Yoshiie's son Yoshitoki adopted the name Ishikawa, after a place in Kawachi province. The Ishikawa later moved to Shimotsuke province, and were known for a few generations as the Oyama, borrowing that name from a local family. They moved to Mikawa Province in the 15th Century and resumed the name 'Ishikawa'. Ishikawa Chikayasu came to serve Matsudaira Chikatada and, afterwards, the Ishikawa would be a notable retainer family of the Matsudaira/Tokugawa.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005