Lifespan: 1/15 of Daiei 7 (1527) to 5/4 of Tenshō (1579)
Other Names: Unakami-kurō (common)
Clan: Unakami → Shimōsa-Chiba
Father: Chiba Masatane
Mother: Daughter of Kaneda Zaeimon-taifu Masanobu
Siblings: Toshitane, Tanetomi
Children: Yoshitane, Kunitane
Chiba Tanetomi served as a bushō during the Sengoku period. He was the twenty-seventh head of the Chiba clan of Shimōsa Province. Tanetomi excelled in diplomatic relations.
Tanetomi was born as the second son of Chiba Masatane, the twenty-fourth head of the Shimōsa-Chiba clan.
Masatane demolished Sugayama Castle and built Moriyama Castle nearby, positioning Tanetomi in this location. While Tanetomi was in Moriyama Castle, he built the Yoshitai Temple below Mount Suga to mourn for his wife.
Initially, Tanetomi inherited the Unakami clan who were members of the Tō, one of six clans who were members of the Six Clans of the Chiba, known as the Chiba-rokutō.
In 1557, his younger brother (or nephew), Chiba Chikatane, was murdered at the hands of his retainers, so Tanetomi succeeded to the headship of the clan. After becoming the head of the clan, he placed Kurihara Nyūdō in Moriyama Castle. Emulating the hōkōshū, or military organ of the Muromachi bakufu, Tanetomi created the Moriyamashū, a group comprised of members of the Chiba family and senior retainers.
In 1560, when Uesugi Kenshin of Echigo Province attacked Ashikaga Yoshiuji, the Koga kubō, Tanetomi responded to a request from Hōjō Ujiyasu to send reinforcements. In 1561, Tanetomi was attacked by Masaki Nobushige, a retainer of the Satomi clan, and he lost Usui and Oyumi castles. That same year, when Kenshin led an army of 110,000 soldiers to attack Odawara Castle, Tanetomi dispatched reinforcements to the Gohōjō clan. Thereafter, he reconciled and attended a ceremony at the Tsurugaoka-Hachiman Shrine for the appointment of Kenshin as the deputy shōgun of the Kantō. He argued with Oyama Takatomo, a sengoku daimyō of Shimotsuke Province, in regard to the lead position in the seating order. Through mediation by Kenshin, Tanetomi took the lead seat.
In 1562, with the support of the Gohōjō clan, Tanetomi recaptured Usui and Oyumi castles from the Masaki clan. At the Siege of Usui Castle, he repelled Kenshin. Thereafter, Tanetomi continued to clash with the Satomi clan and, in 1571, he fought against Satomi Yoshihiro at Oyumi Castle. In 1579, Tanetomi died at the age of fifty-three. Tanetomi was succeeded by his eldest son, Chiba Yoshitane, who was born as a twin along with Chiba Kunitane.
By deepening his relationship with the Gohōjō clan, Tanetomi was able to repel attacks by Uesugi Kenshin, the Yūki, and the Satomi. Tanetomi prevailed in battles against many opponents including Takeda Shingen, Uesugi Kenshin, Ashikaga Yoshiuji (the Koga kubō), the Satake clan, and the Satomi clan, expanding the power of the main branch of the Chiba clan.
At the Kairin Temple in the city of Sakura, there is a group of stone monuments from the Middle Ages, one of which includes an inscription with a prayer for Tanetomi. There is another monument for Tanetomi included among a cluster of monuments at the Shōin Temple in Ōsakura in the city of Sakura in Chiba Prefecture.