The Koyanagawa clan (小梁川氏, Koyanagawa-shi) was a samurai family in Japan descending from the Date clan, a daimyo (feudal lord) family in Mutsu Province.
[1] However, this is considered impossible because not only the elder brother and 12th clan head, Date Narimune, but also Date Mochimune (died in 1469) were still alive at this time.
[2] In 1591, Date Masamune moved to Iwadeyama due to the Kasai Ōsaki Rebel, when the old territories of Nagai and Date were seized.
During the Edo period, the Koyagawa clan further moved to Notezaki within the same province, and after that, the clan ruled the area until the Meiji Restoration.
The patriarch of the Koyanagawa clan, Koyanagawa Morimune, was the third son of Date Mochimune, the 11th head of the Date clan.