Sakai Tadakatsu (酒井 忠勝, 1594 – November 13, 1647) was a Japanese daimyō of the early Edo period. Tadakatsu and his descendants are linked in the history of the han at Tsuruoka (Shōnai) in Dewa Province.
The Sakai were identified as one of the fudai or insider daimyō clans which were hereditary vassals or allies of the Tokugawa clan, in contrast with the tozama or outsider clans.
Tadakatsu was part of the senior branch of the Sakai.
The fudai Sakai clan originated in 14th century Mikawa Province. The Sakai claim descent from Minamoto Arichika. Arichika had two sons: one of them, Yasuchika, took the name Matsudaira; and the other son, Chikauji, took the name Sakai—and this samuari ancestor is the progenitor of this clan's name.
Sakai Hirochika, who was the son of Chikauji, had two sons, and their descendants gave rise to the two main branches of the Sakai clan.
The Senior branch of the Sakai, are descendants of Sakai Tadatsugu (1527–1596), who was a vassal of Tokugawa Ieyasu. Tadatsugu was charged with the defense of Yoshida Castle in Mikawa province.
In 1578, Sakai Ietsugu (1564–1619) succeeded to his father's role as defender of Yoshida Castle. The Ie- in the beginning of Ietsugu's name was a special honor bestowed by Tokugawa Ieyasu, who intended to emphasize bonds of loyalty with those who were allowed to share in any part of his name.
When Ieaysu's holdings were transferred to the Kantō in 1590, Ietsugi was installed at Usui Domain (30,000 koku) in Kōzuke Province ; in 1604, removed to Takasaki Domain (50,000 koku) in Kōzuke Province ; in 1616, removed to Takata Domain (100,000 koku) in Echigo Province ; in 1619, removed to Matsushiro in Shinano Province; and then, in 1622 through 1868, installed at Tsurugaoka Domain (120,000 koku) in Dewa Province.
The head of this clan line was ennobled as a "Count" in the Meiji period.
Sakai Tadakatsu of Shōnai Domain came from the same family as the synonymous, contemporary daimyō of Obama, Sakai Tadakatsu, but should not be confused with him.
Tadakatsu was the eldest son of Sakai Ietsugu, who was in turn the son of Sakai Tadatsugu, one of Tokugawa Ieyasu's three most trusted generals.
After brief tenures as daimyō of Takada Domain and Matsushiro Domain, Tadakatsu was transferred to the new Shōnai Domain in the summer of 1622. He retired in 1634, yielding his position to his son Sakai Tadamasa.
Tadakatsu died in 1647, at age 53.