Lifespan: Tenshō 6 (1578) to 4/20 of Kanei 5 (1628)
Titles: Junior Fifth Rank, Senior Assistant Minister of Military Affairs
Lord: Tokugawa Ieyasu → Tokugawa Hidetada → Tokugawa Iemitsu
Father: Sengoku Hidehisa
Mother: Honyōin (daughter of Nonomura Yukinari)
Siblings: Hisatada, Hidenori, Tadamasa, Masayoshi, Masanao, Hisataka
Wife: [Formal] Daughter of Kobori Masanori
Children: Masatoshi, Masanori, Masakatsu, daughter (wife of Kuwayama Kazuharu), daughter (wife of Mizuno Katsutada)
Sengoku Tadamasa served as a daimyō and, during the early Edo period, as the second head of the Komoro domain in Shinano Province.
Tadamasa was born in 1578 as the third son to Sengoku Hidehisa, a retainer of Hashiba Hideyoshi. His eldest brother, Hisatada, was blind so given special status as a kengyō. His second eldest brother, Hidenori, participated on behalf of the western army in the Battle of Sekigahara in 1600, and, after the war, was disowned by his father and removed from his apparent role as heir. As a consequence, Tadamasa became the successor to his father.
Tadamasa and Hidehisa together served Tokugawa Ieyasu, joining the eastern army in the Battle of Sekigahara, including in an attack against Sanada Masayuki at Ueda Castle in Shinano Province, known as the Battle of Ueda. To recognize their contributions, Tadamasa received one of the characters in his name from Tokugawa Hidetada, thereby changing his name from Hisamasa to Tadamasa. Tadamasa was further awarded the title of Junior Fifth Rank and Senior Assistant Minister of Military Affairs and assigned the corresponding duties.
In 1614, Tadamasa became head of the clan in the wake of his father’s death, and became the second head of the Komoro domain with a fief of 50,000 koku. He participated in the Winter Campaign of the Siege of Ōsaka against Toyotomi Hideyori, responsible for one of the entrances. In 1615, during the Summer Campaign, he fought against Toyotomi forces led by Sanada Nobushige and Mōri Katsunaga at the Battle of Tennōji and Okayama. Despite enduring a fierce attack from the Mōri units, he captured eleven heads. Owing to his loyalty and contributions on the battlefield, on 9/25 of 1622, his fief was increased by 60,000 koku and he was assigned to Ueda in Shinano Province.
Tadamasa aimed to stabilize his territory, encouraging the return of local citizens and wandering samurai who had fled the area during the time that his father practiced an authoritarian style of governance while serving as the lord of Komoro Castle. He also worked to adopt reforms including the conversion from a currency-based system to a rice-based system of remuneration. During his time as the lord of Ueda Castle, he followed after the Sanada, promoting the development of new arable lands and industries, along with policies to separate those engaged in the military from the peasant farmers. He strengthened his governance by appointing a village leader for each of the eight townships comprising his territory. From 1626, Tadamasa engaged in a major renovation of Ueda Castle; prior to its completion, however, he died in 1628. Tadamasa was succeeded by his eldest son, Sengoku Masatoshi.