It is said that the origin of the clan can be traced back to the time when Tanemichi KOKUBUN from Shimousa Province moved to Kokubun-no-sho (国分荘), Miyagi County, which was given to him as reward grants for the Battle of Oshu.
下総国出身の国分胤通が宮城郡国分荘を奥州合戦の恩賞として与えられて移住したのがはじまりだと伝える。