However, this connection is tenuous and not backed by documentary evidence, suggesting that the Iwaki were instead descendants of the local Kuni no miyatsuko, and adopted the legend of Taira descent for greater prestige.

During the Heian period, they controlled territory in what is now the city of Iwaki, Fukushima and had close ties with the Northern Fujiwara of Hiraizumi.

The 15th hereditary chieftain, Iwaki Shigetaka was pressured by Sōma Akitani into giving his daughter, Kubo-hime, as wife to Date Harumune and accepting the son of this union as his heir.

At the time of the Battle of Sekigahara, although the Iwaki clan supported the Eastern Army of Tokugawa Ieyasu, the Satake clan remained neutral, and Iwaki Sadataka obeyed the orders of his older brother, Satake Yoshinobu not to attack the forces of Uesugi Kagekatsu in Aizu Domain.

Ieyasu was petitioned by Doi Toshikatsu, Honda Tadanobu and about 300 other samurai officials to show clemency to Iwaki Sadataka, and he was permitted fight in the 1614 Osaka Summer Campaign, for which he was awarded 10,000 koku domain in Shinano Province the following year.