Ishikawa Kazumasa

In this Japanese name, the surname is Ishikawa.

Ishikawa Kazumasa 石川 数正
Ishikawa Kazumasa in Nagashino
Born	1534 (1534)
Died	1609 (aged 74–75)
Allegiance	Ishikawa clan Imagawa clan Tokugawa clan Toyotomi clan
Battles / wars	Battle of Mikatagahara Battle of Nagashino Battle of Komaki and Nagakute

Ishikawa Kazumasa (石川 数正, 1534–1609) was a Japanese notable retainer under Tokugawa Ieyasu, who served him since childhood, when they were both hostages under the Imagawa.

After 1560, when Ieyasu abandoned the Imagawa, Kazumasa then became a valued retainer and administrator under him. In 1562, when Ieyasu managed to convince Imagawa Ujizane to release his family, Kazumasa acted as guardian of the Imagawa, which at the time was a very dangerous task.

By 1567, the majority of daimyō forces in the Tokugawa armies were organized in two divisions, each with a separate commander. Kazumasa was placed over the forces of 13 Tokugawa daimyō-vassals and his counterpart, Sakai Tadatsugu, was given command over the forces of 18 daimyō-vassals. He participated in the 1572 Battle of Mikatagahara. and 1575 Battle of Nagashino.

After Toyotomi Hideyoshi's victory over Shibata Katsuie in 1583, Ieyasu expressed his congratulations to Hideyoshi through Kazumasa. Later, Kazumasa and Sakakibara Yasumasa accordingly issued statements attacking Hideyoshi, due to the Tokugawa's decision. Kazumasa served at the Komaki headquarters during the Komaki-Nagakute Campaign.

In 1585, Kazumasa, very dismayed by what he saw as Tokugawa's foolhardy path of resistance against Toyotomi Hideyoshi, switched sides to Hideyoshi. This inconvenienced Ieyasu, who had to reconstruct his military organization and defensive policies, since Kazumasa had significant knowledge about their organization.

Kazumasa then later decided to retire and live with his son Ishikawa Yasunaga, until he died in 1609.