According to genealogical tables of the Kokubun family of Mutsu Province, Tanemichi became the founder of the family after getting the Kokubun-sho estate as a reward of the Battle of Oshu.
陸奥の国分氏の諸系図は、下総出身の胤通が奥州合戦の恩賞で陸奥の国分荘を得て国分氏の祖になったとする。