The Sakai (Japanese 酒井氏, Sakai-shi) were a family of the Japanese sword nobility (Buke), descended from Minamoto no Arichika (Seiwa Genji). Arichika had two sons, one of whom, Yasuchika (奏親), took the name "Matsudaira" and the other, Chikauji (親氏), took the name "Sakai".
Hirochika (広親), the son of Chikauji, had two sons who established the two main branches of this family.
With the fiefs of Himeji, Tsuruoka and Obama, each with over 100,000 koku, the Sakai are among the larger Fudai-Daimyō of the Edo period.
Sakai Clan The six lines
Ujitada (氏}忠) lineage.
Ietsugu (家次, 1564-1619) succeeded his father Tadatsugu in 1578 and took over Yoshida (Mikawa) Castle. When Tokugawa Ieyasu took over the Kantō region in 1590, he provided Ietsugu with an income of 30,000 koku in Usui (Kōzuke). In 1604 he moved to Takasaki (Kōzuke) with an income of 50,000 koku, and in 1616 to Takada (Echigo), 100,000 koku. After moving to Matsushiro (1619), Ietsugu took over the fief of Tsuruoka[Note 2] (Dewa), also called "Shōnai" (庄内), where his descendants served as Daimyō with an income of 120,000 koku until the Meiji Restoration. After the Meiji Restoration, the head of this line held the title of Count until 1945.
Sakai Tadaaki (忠発; 1812-1876), on the Tokugawa side in northern Japan, was one of the last Daimyō to bow to the new Meiji government, but his son Tadazumi (忠篤; 1853-1915) was fascinated by Saigō Takamori and pursued military training under him. In 1872, Tadazumi was sent to Berlin for further training and remained there for seven years. He was followed a year later by his brother Tadamichi (忠宝; 1856-1921), who also stayed there for seven years. 
A branch line resided at Matsuyama (Dewa) with an income of 20,000 koku. Vice Count.
Ietada (家忠) lineage.
Shigetada (重忠; 1564-1619) received Kawagoe (Musashi) in 1590 with 15,000 koku, then Umayabashi (Kōzuke) in 1601 with 35,000 koku. During the Ōsaka campaign he took over the guard of Edo Castle. Tadakiyo (忠清, 1626-1681) took charge of the shogunate during Tokugawa Ietsuna's illness, excelling in administration. His descendants were transferred to Himeji (Harima) in 1749 with an income of 150,000 koku. There the Sakai resided until the Meiji Restoration.[Note 3] The last daimyō was Tadakuni (忠邦; 1854-1878). Count after 1868.
A collateral line of this line, beginning with Tadahiro, resided at Isesaki (Kōzuke) from 1681 until the Meiji Restoration with 20,00 koku. Vice Count.
Tadatoshi (忠利, 1562-1627) received Tanaka (Suruga) in 1601 with 10,000 koku. He then transferred to Kawagoe with 30,000 koku.
Tadakatsu (忠勝; 1587-1662), son of Tadatoshi, was transferred to Obama (Wakasa) in 1634, where the descendants resided with an income of 103,000 koku until the Meiji Restoration. Count thereafter.
A collateral line resided at Tsuruga (Echizen) with 10,000 koku. Vice count.