The Okochi clan is part of the Seiwa-Genji (Minamoto clan) and Settsu-Genji (Minamoto clan), and is said to have been established when Akitsuna, the grandson of MINAMOTO no Yorimasa, moved to Okochi-go, Nukata County in Mikawa Province (which some have asserted to be the present-day Aza-Okochi, Ohira-cho, Okazaki City, Aichi Prefecture) and called himself Okochi.
大河内氏（おおこうちし）は、清和源氏、摂津源氏の一族で、源頼政の孫、顕綱（あきつな）が三河国額田郡大河内郷（愛知県岡崎市大平町字大河内・注、異説あり。洞町等）に移り住み、大河内氏を称したことを始まりとする。