Lifespan: Bunan 3 (1446) to 12/6 of Meiō 2 (1494)
Lord: Ashikaga Yoshimasa → Ashikaga Yoshihisa → Ashikaga Yoshiki
Father: Chiba Tanekata
Siblings: Sanetane, Yoritane
Children: Moritane (adopted)
Chiba Yoritane served as a bushō from the middle of the Muromachi period into the Sengoku period. Yoritane was the second head of the Musashi-Chiba clan (recognized as head of the Chiba clan by the Muromachi bakufu).
In the Kyōtoku War, those who sided with Ashikaga Shigeuji (the Koga kubō), including a senior retainer named Hara Tanefusa, and family members including Makuwari Yasutane, Chiba Tanenao (an uncle), Chiba Tanenobu (a cousin), and Chiba Tanekata (father) were all killed. Yoritane fled with his older brother, Chiba Sanetane, to Ichikawa Castle in the Yawata-no-shō manor of Shimōsa Province. Yoritane received support from Ashikaga Yoshimasa, the eighth shōgun of the Muromachi bakufu, who sent Tō Tsuneyori (a member of the hōkōshū or military members under the direct control of the bakufu), but these forces lost to Yanada Mochisuke sent by Shigeuji. Early in 1456, Ichikawa Castle fell and Yoritane fled to Musashi. That same year, Tsuneyori killed Makuwari Yasutane and Makuwari Tanemochi (father and son), and Hara Tanefusa also fled.
Meanwhile, Yoritane became the lord of Akatsuka Castle and his older brother, Sanetane, the lord of Ishihama Castle. In the spring of 1457, pressure continued on the Koga kubō through means such as the construction of Edo Castle by Ōta Dōkan, the kasai, or head of house affairs for the Ōgigayatsu-Uesugi family and a maternal relative of Yoritane. Yoritane, however, did not possess a definitive territory so were pressed economically, making a return to Shimōsa improbable.
Thereafter, Yoritane’s older brother, Sanetane, retired and Yoritane became the lord of Ishihama Castle and garnered recognition from the bakufu as head of the Chiba clan. Nevertheless, acts of resistance continued such as the construction of Motosakura Castle by Iwahashi Suketane, lord of the village of Iwahashi in Intō-no-shō, a manor in the Inba District of Shimōsa. Suketane was a member of a cadet family of the Chiba. His son, Chiba Noritane, proclaimed himself the head of the Chiba clan. Meanwhile, owing to his dependence upon Noritane, Ashikaga Shigeuji, who was in conflict with the bakufu, recognized him as the head of the Chiba clan, undermining Yoritane’s plans to return to Shimōsa. In the spring of 1469, Tō Tsuneyori lost his territory in Mino Province to Saitō Myōchin in the Ōnin Conflict whereupon he left his son, Tō Yorikazu, in Shimōsa and returned to the capital of Kyōto, reducing his military power there.
Early in 1478, the Yamauchi-Uesugi family and Ōgigayatsu-Uesugi family reconciled with Shigeuji. Noritane joined with Nagao Kageharu to oppose the settlement. With the consent of Shigeuji, and the backing of Ōta Dōkan, Yoritane initiated a plan to eliminate Noritane and achieved victory at the Battle of Sakainehara. Noritane called together his forces and retreated to Usui Castle, but, in the summer of 1479, Yoritane toppled Usui and took control of a majority of Shimōsa and Kōzuke provinces. Nevertheless, over a period of twenty years, the system of governance for Chiba had already been established by Suketane and Noritane. Yoritane lacked support in these provinces and, after being swept-up in internal disputes among the Uesugi clan, was forced to retreat. As a result, the descendants of Noritane became the successors to the Chiba clan in Shimōsa while the descendants of Yoritane settled in Musashi, devolving into kokujin, or local families of limited influence.