It is said that the Kokubun clan (in Mutsu Province) was samurai who had possessed the southern part of Miyagi County, Mutsu Province from the period of the Northern and Southern Courts to the Sengoku period (the period of warring states), and this clan originated from Tanemichi, who took his family name from Kokubun in Shimousa Province and relocated to Kokubun in Miyagi County, which was given to him as reward grants for the Battle of Oshu.
国分氏(陸奥国)は、南北朝時代(日本)から戦国時代(日本)まで陸奥国宮城郡南部を領した武士で、下総国の国分から氏をとった国分胤通が宮城郡国分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。