Lifespan: 10/12 of Tenbun 11 (1542) to 6/3 of Keichō 11 (1606)
Other Names: Yagorō (childhood), 方休 (monk’s name)
Rank: bushō, daimyō
Title: Junior Fifth Rank (Lower), Governor of Ise, Vice Minister of Military Affairs, Master of the Western Capital Office
Domain: lord of Hitachi-Shimodate
Lord: Yūki Harutomo → Yūki Hideyasu → Tokugawa Ieyasu → Tokugawa Hidetada
Father: Mizunoya Harutoki
Adoptive Father: Mizunoya Masamura
Siblings: Masamura, Katsutoshi
Wife: [Formal] Daughter of Hotta Masayoshi
Mizunoya Katsutoshi served as a bushō and daimyō from the Sengoku to early Edo period. He was the first lord of the Shimodate domain in Hitachi Province.
In 1542, Katsutoshi was born as the second son of Mizunoya Harumochi. In 1566, Katsutoshi, together with his older brother, Mizunoya Masamura, followed Yūki Harutomo in battle against Uesugi Kenshin of Echigo Province. In 1569, following the retirement of Masamura, Katsutoshi inherited the headship of the clan.
In 1585, Katsutoshi, together with Masamura, captured Tano Castle in Shimotsuke Province, expanding their authority in the direction of Shimotsuke. After the Conquest of Odawara, he became a yoriki-daimyō, or daimyō serving as a security officer, for the Yūki clan. When discussion arose concerning the adoption of Hideyasu (the second son of Tokugawa Ieyasu) by Yūki Harutomo, owing to preexisting cordial relations between Masamura and Ieyasu, Katsutoshi joined negotiations with the Tokugawa clan. During the Bunroku-Keichō Campaign beginning in 1592, Katsutoshi was stationed at Nagoya Castle in Hizen Province.
In 1600, at the Battle of Sekigahara, as a younger cousin of Minagawa Hiroteru, he joined the Eastern Army. At this time, his son, Mizunoya Katsutaka, was taken hostage by the Western Army. After the war, Katsutoshi received recognition of his rights to his territory based on his contributions to keep in check Satake Yoshinobu in Shimotsuke. After the transfer of Tokugawa Hideyasu to Kita-no-shō in Echizen Province, Katsutoshi formally became an independent daimyō. In lieu of Katsutoshi, his nephew, Masayoshi, served Hideyasu and followed him to Echizen.
On 6/3 of Keichō 11 (1606), Katsutoshi died at the age of sixty-five. He was succeeded by his eldest son, Katsutaka.