Ueda Castle
Tadataka was born in Kamiwada, Mikawa Province, the son of Tokugawa retainer Ōkubo Tadakazu. His older brother was Ōkubo Tadayo. He joined Tadayo at age 17 for his first campaign, during the subjugation of Tōtōmi Province. Tadataka's first battle was the siege of Inui Castle. From then on, he fought in many battles, under Tadayo or his other brother, Ōkubo Tadasuke. Tadataka served with distinction at the Battle of Takatenjin Castle, taking the head of enemy general Okabe Motonobu. He also fought at the siege of Ueda Castle. After the Siege of Odawara, when Tokugawa Ieyasu moved to the Kantō Region, he granted Tadataka land assessed at 3,000 "koku", and appointed him "yari-bugyō" (magistrate of spears) in the Tokugawa main battle camp.