- Birth: 1565
- Death: 1613
- Titles: Harima no kami, Shinano no kami, Yamato no kami
- Sons: Koide Yoshihide (1586-1668), Koide Ise no kami Yoshichika
Yoshimasa was the son of Koide Hideharu and the nephew of Toyotomi Hideyoshi's wife. At first the lord of Tatsuno castle in Harima province, he was granted 53,000 koku worth of land in Tajima province in 1595 following Hideyoshi's censure of a number of Toyotomi Hidetsugu's intimates. He sided with Ishida Mitsunari during the Sekigahara Campaign (1600) and joined in the siege of Tanabe in Tajima. After Mitsunari was defeated, Yoshimasa kept his lands thanks to the efforts of his younger brother Koide Hideie, who had fought on the Tokugawa side.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005