His adoptive family, the Ishii family originated by Tadakyo ISHII who was a cousine of Yotaiin, the legal wife of Naoshige NABESHIMA, the originator of Saga Domain.
養家の石井家は、佐賀藩祖鍋島直茂の正室陽泰院の従弟石井忠教を祖とする家筋。