According to the genealogical table, his father was Tanemochi KOKUBUN, his mother a daughter of Taira no Naotsune, and he had a younger brother, Shigeharu, and two sisters who became the wives of Yasutane TAKEISHI and Yorikuni MUTO, respectively.
その系図によれば胤重の父は国分胤茂、母は平直常の女、弟に茂晴があり、姉妹が2人いてそれぞれ武石泰胤と武藤頼国の妻になった。