The Ishikawa genus (石川氏, Ishikawa-shi) is a Japanese samurai family descended from the Seiva Genji lineage (Minamoto dynasty).
The ancestor of the Ishikawa clan is Minamoto Yoshitoki, the son of Minamoto no Yoshihie.
The clan took its name from Ishikawa district of Kawachi province. During the Sengoku period, the Ishikawa clan divided into two main lines: one of them, settled in the 15th century in Mino province, became vassal of the Tokugawa dynasty.
Ishikawa Kazumasa (1534-1609), one of the main samurai of Tokugawa Ieyasu, defected to Toyotomi Hideyoshi in 1585. In 1590, Ishikawa Kazumasa took possession of the domain of Matsumoto in the province of Shinano (100 000 koku).
In 1592, Kazumasa gave the power in the principality to his elder son Yasunaga (1554-1643). In 1613, Ishikawa Yasunaga was accused of having participated in Okubo Yasunaga's conspiracy and stripped of his property.
The Mikawa-Ishikawa line was continued by Ishikawa Ienari, Kazumasa's uncle. Ienari's descendants ruled over the Ise-Kameyama domain during the Edo period.
Another lineage of Ishikawa clan, originating from Kawachi province, became the ancestor of Nakagawa clan, which ruled in Oka-han during Edo period.