Imagawa clan
Torii was born in Okazaki, the son of Torii Tadayoshi. As a boy, he was sent as hostage to the Imagawa clan, together with the future Tokugawa Ieyasu. The young Mototada served the then-Matsudaira Takechiyo as a page. After Ieyasu's return from the Imagawa clan, and his unification of Mikawa Province, Mototada served as one of his chief generals.