It is transmitted that the clan was established when Tomoyasu II, an adopted child of Totomi kokushu (daimyo of Totomi) FUJIWARA no Tomosuke, who was the sixth grandchild of FUJIWARA no Fuyutsugu, moved to the land of Iinoya.
藤原冬嗣6代孫の遠江国守藤原共資の養子、井伊共保が井伊谷の地へ移ったことに興ると伝える。