The Minakuchi Domain was founded in 1682 by Akitomo KATO, a tozama (outsider feudal lord) of the Yoshinaga Domain in Iwami Province (with a fief yielding 10,000 koku of rice), who became the lord of the Minakuchi-jo Castle in Omi Province with 10,000 koku of rice increased to 20,000 in total because of the military exploit by himself and his grandfather, Yoshiaki KATO, known as one of the seven excellent military commanders in Hideyoshi's army at the battle of Shizugatake (Shizugatake-no-shichihon-yari).
天和(日本)3年（1682年）、賤ヶ岳の七本槍の1人として知られる加藤嘉明の孫で、外様の石見国吉永藩（1万石）藩主・加藤明友が祖父と自身の功により1万石の加増を受け、2万石で近江国水口城主となり立藩。