This family line began when a grandson of Toshisada ODA from the Oda clan was adopted into the Inoo clan, a powerful local clan in Owari, and changed his name to Sadamune INOO (also pronounced IINOO).
織田氏の一族織田敏定の孫が尾張の土豪飯尾氏の養子となり、飯尾定宗と名乗ったことに始まる。