Odai was born into a wealthy family as the daughter Tadamasa MIZUNO and his wife Keyoin at her father's Ogawa-jo Castle in Chita District, Owari Province (Ogawa, Higashiura-cho, Chita County, Aichi Prefecture).
於大は尾張国知多郡の豪族水野忠政とその夫人華陽院の間に、父・忠政の居城緒川城（愛知県知多郡東浦町緒川）で生まれた。