In the early Edo period, Ōzu was part of the territory of Tōdō Takatora, who had rebuilt Ōzu Castle. In 1608, the Tokugawa shogunate promoted him to Tsu Domain in Ise Province and created the 53,000 koku Ōzu Domain for Wakisaka Yasuharu from Sumoto Domain on Awaji island.  In 1617, his son Yasumoto was transferred to Iida Domain in Shinano Province and Ōzu was reassigned to Katō Sadayasu from Yonago Domain, with an increased kokudaka to 66,000 koku. Sadayasu died suddenly in 1623 without formally having appointed an heir, which would normally be cause for attainder; however, his eldest son Katō Yasuaki managed to secure an audience with Shogun Tokugawa Hidetada and was accepted as heir. However, the shogunate also allowed his younger brother, Katō Naoyasu, to carve out a 10,000 koku portion of the estate and to establish Niiya Domain and a cadet brach of the clan. This move was vehemently opposed by Ōzu Domain, and relations between the two branches of the clan was hostile for the next two centuries. Niiya Domain was left in the ambitious position of both being a subsidiary domain of Ōzu and a direct domain under the shogunate.