Lifespan: Eishō 7 (1510) to 8/28 of Tenbun 2 (1533)
Other Names: 祐修, 祐裔
Rank: sengoku daimyō
Title: Governor of Yamato
Father: Itō Tadasuke
Mother: Daughter of Fukunaga Sukeaki
Siblings: Sister (wife of Fukunaga Genpei), son (birth mother from the Nakamura clan), Sukemitsu, Yoshisuke, Gyokuren-fujin (wife of Shimazu Tadaharu), Sukeyoshi
Wife: Daughter of Hongō Tadasuke
Itō Sukemitsu served as a bushō and sengoku daimyō during the Sengoku period. Sukemitsu was the ninth head of the Hyūga-Itō clan.
In 1510, Sukemitsu was born as the son of Itō Tadasuke. In the latter years of his life, Tadasuke was absorbed in conflict with the Hongō clan including for control of Nonomidani Castle in Hyūga Province.
The connection between the Hongō clan and Nonomidani Castle extended back over a century. In the Ōei era (1394 to 1428), Shimazu Motohisa and Hongō Yoshihisa toppled Nonomidani and Kabayama Narihisa became the lord of the castle. In 1521, after Kabayama Nagahisa moved to Obama in Ōsumi Province, the castle came under the control of the Hongō and Hongō Naohisa became the lord. Two years later, in 1523, Tadasuke allied with the Kitahara clan and, with a large army, launched a successful assault to capture the castle. Later that same year, Tadasuke suddenly died and, at a young age, Sukemitsu inherited the headship of the clan. Meanwhile, Sukemitsu’s uncle, Itō Sukemune, died of illness one month after Tadasuke so Sukemitsu’s maternal grandfather and chief retainer, Fukunaga Suekaki, and his maternal relatives in the Fukunaga clan seized the governing powers of the Hyūga-Itō clan.
In 1528, the Itō attacked the Niiro clan.
Around this time, the Itō controlled the southern portions of Hyūga and engaged in persistent clashes with the Hongō clan based at Miyakono Castle. The Hongō allied with their original house, the Shimazu clan, and sought to restore their power. Although the superior position of the Itō vis-à-vis the Hongō as built in the era of Itō Tadasuke did not change, in 1531, Sukemitsu reconciled with the Hongō on the condition that he return Nonomidani Castle to the Hongō and wed the daughter of Hongō Tadasuke (written with different characters than Itō Tadasuke).
In the era of Sukemitsu, the authority of the Itō grew significantly, but the family circumstances were unstable. Owing to grievances with the autocratic style of the Fukunaga, a retainer named Inazu 重由 initiated an event known as the Wakashū Rebellion. In 1531, the Hongō allied with the Shimazu and Kitahara clans to oppose the Itō, escalating into a battle at Mimata-in-Taka Castle that resulted in a major defeat for the Itō.
In 1533, after the early death from illness of Sukemitsu, his uncle, Itō Suketake revolted, forcing Fukunaga Sukeaki and his three sons to kill themselves and then he occupied Tonokōri Castle. This is known as the Bushū Revolt. In the background, Sukeaki had formerly leveraged the authority of Sukemitsu in an effort to oust and eliminate a significant number of opposition elements.