Lifespan: 15xx to 2/5 of Eiroku 9 (1566)
Father: Mimura Munechika
Siblings: Iechika, Chikanari
Wife: [Formal] from the Ogasawara branch of the Awa-Miyoshi clan
Children: Shō Motosuke, Motochika, Motonori, Ueda Sanechika, daughter (wife of Ueno Takanori), daughter (wife of Narasaki Motokane), daughter (wife of Mizuno Katsunari), daughter (wife of Ishikawa Hisanori)
Mimura Iechika served as a daimyō during the Sengoku period. Iechika was the lord of Kakushu Castle and, later, Bitchū-Matsuyama Castle in Bitchū Province.
Iechika was the son of Mimura Munechika and grandson of Mimura Morichika. His formal wife was a daughter from the Ogasawara branch of the Awa-Miyoshi clan. She was the mother of Mimura Motochika and Ueda Sanechika.
In Bitchū Province, the authority of the Hosokawa family who served as military governors was in decline while the kokujin class, or provincial landowners, were on the rise. Initially, the Shō clan was allied with the Hosokawa. Later, in the era of Shō Tamesuke, the Shō came into conflict with the Mimura and expanded their base of power. After the Shō allied with the Amago clan, their power-struggle with the Mimura reached its limit. The Mimura then became the first local landowners in Bitchū to request support from the Mōri clan of Aki Province. Mōri Motonari had a favorable impression of Iechika, and gladly proclaimed to a messenger from the Mimura that their request equated to control of Bitchū by the Mōri. After allying with the Mōri clan, the Mimura expanded their influence in Bitchū.
In 1561, the Mimura defeated Shō Takasuke (who had the support of the Amago), advanced to Bitchū-Matsuyama, and became the preeminent power in Bitchū. Iechika then moved his base of operations from Kakushu Castle in Nariwa to Bitchū-Matsuyama Castle and assigned Kakushu Castle to his senior retainer, Mimura Chikanari. During this period, Iechika promoted political marriages with families serving as deputy military governors of Bitchū, including the Shō, the Ishikawa, and the Ueno; however, owing to ongoing hostilities, the Shō were not receptive to political marriage between the families.
In 1564, after Iechika sent forces under Ishikawa Hisatomo to support the Saisho clan at Tatsunokuchi Castle in Bizen who were allied with the Mimura, Shō Takasuke and Shō Katsusuke abandoned the Mimura. In a bid to further expand their domain, Iechika invaded Bizen and Mimasaka provinces, and, in 1565, attacked Gōtō Katsumoto at Mitsuboshi Castle in Mimasaka. Owing to support from the Uragami and Ukita Naoie, the attack failed, but, he entered Mimasaka again the following year and toppled castles under Ukita control. In the second month of 1566, while engaging in deliberations with his senior retainers at the Kōzen Temple in the village of Momi in Mimasaka, Iechika was shot and killed by matchlocks wielded by Endō Hidekiyo and his brother, Endō Toshimichi, ordered by Ukita Naoie. At the time, this marked a rare assassination by firearms.
Miura Sadahiro took advantage of this opportunity to recapture his landholdings in Mimasaka from the Mimura.