Iwakuni was formerly the castle town of the Iwakuni han, which was formed by Lord Hiroie Kikkawa after he was banished there for supporting the defeated shogun. The Kikkawa clan ruled the han during the Edo period. The han was originally assessed at 30 thousand koku, and later, 60 thousand. Iwakuni han prospered for 300 years up until the Meiji Restoration. Before being re-founded with the same name following the mergers in 2006, the city was first founded on April 1, 1940.
On March 20, 2006, the old city of Iwakuni absorbed the towns of Kuga, Mikawa, Miwa, Nishiki, Sh?t? and Y?, and the village of Hong?, all from Kuga District, to form the new, expanded city of Iwakuni
