Hitachi Province
Nishio Tadayoshi was the fourth son of Makino Sadanaga, daimyō of Kasama Domain in Hitachi Province. He became the adopted heir of the fourth daimyō of Yokosuka Domain, Nishio Tadayuki, in 1783 and married Tadayuki's daughter. Tadayoshi became daimyō and head of the Nishio clan after his adoptive father's death in 1801.