Shigemitsu was the second son of Izumida Kagetoki. He succeeded his elder brother Izumida Mitsutoki, who was killed fighting the Sôma clan in 1582, at Iwanuma castle and enjoyed an income of 8,000 koku. Shigemitsu assisted in the siege of Nihonmatsu Castle (1585) and in 1588 jointly commanded 5,000 men with Rusu Masakage against the Ôsaki but was defeated and captured. He was allowed to return to the Date later that year and went on to serve Date Masamune in various other campaigns. He accompanied Masamune to Hideyoshi's Korean Invasion headquarters on Kyushu and died in 1596.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005