was a feudal domain under the Tokugawa shogunate of Edo period Japan, in what is now southeastern Yamaguchi Prefecture. It was centered around Iwakuni jin'ya and was ruled throughout its history the Kikkawa clan. Iwakuni Domain was dissolved in the abolition of the han system in 1871.
Kikkawa Hiroie was the grandson of Mà Âri Motonari. At the Battle of Sekigahara in 1600, Kikkawa Hiroie secretly communicated with Tokugawa Ieyasu, providing the Eastern Army with vital intelligence and blocked the movement of Mà Âri clan forces, preventing them from entering into combat. Despite this, after the battle, Ieyasu was determined to destroy the Mà Âri clan, as they controlled ten provinces in western Japan. Kikkawa Hiroie negotiated a settlement which enabled the Mà Âri to retain at least the two provinces of Suà  and Nagato, even though this cost him his own fief in Izumo Province of 140,000 koku. In return, the Mà Âri granted him the area around Iwakuni, with an assessed kokudaka of 30,000 koku, which was later increased to 60,000 koku. In 1615, Iwakuni Castle was demolished according to the one country, one castle ordinance issued by the shogunate, and a jin'ya was constructed as the clan residence at the base of the mountain where the castle was located.
Iwakuni Domain was nominally a sub-domain of Chà Âshà « Domain and was not recognized by the shogunate and an official domain; the Kikkawa clan was not subject to sankin kà Âtai and was not given the title of daimyà Â. They were also denied the courtesy titles and nominal court ranks normally granted to daimyà Â. However, the clan did maintain a residence in Edo as they had to make tributes of the four seasons to the Shogun and had to visit Edo Castle for a formal audience on the succession of each clan chieftain. During these audiences, they were placed in the same Yanagi-no-ma chamber together with small and middle-ranked tozama daimyà Â. For all practical purposes the domain was independent of Chà Âshà « Domain, and Chà Âshà « Domain officially referred to the domain as "Iwakuni Territory". The Mà Âri regarded the Kikkawa as their retainers despite the fact that the Tokogawa shogunate granted them special consideration. Due to this ambiguous position, relations were often strained between Chà Âshà « and Iwakuni until near the end of the Bakumatsu period.
Kikkawa Hiroie died in 1625 and his son Kikkawa Hiromasa became daimyà Â. He tried to keep independent of Chà Âshà « and has a falling out with Mà Âri Hidenari in 1634. In 1640, he established paper-making as a domain monopoly to raise funds. His son and successor Kikkawa Hiroyoshi devoted himself to cultural projects, and in 1673 the famous Kintaikyà  Bridge. Kikkawa Hironori, the fourth daimyà Â, engaged in extensive land reclamation projects and under his management, the domain became very prosperous. This further aroused the envy of Chà Âshà «, which was suffering from financial difficulties. During the tenure of Kikkawa Hiroyoshi and Kikkawa Tsunenaga, the fifth and sixth daimyà Â, the conflict worsened. Under the seventh daimyà Â, an unsuccessful effort to obtain official recognition as an independent domain failed, and finances deteriorated due to poor harvests. Conditions fluctuated in the late Edo period, but the 10th daimyà Â, Kikkawa Yoshikawa succeeded in financial reforms by carrying out land reclamation projects. In the early Bakumatsu period, although there were a number of Sonnà  jà Âi incidents, the domain initially supported the shogunate. During the Chà Âshà « expeditions, Kikkawa Tsunemoto, the 12th daimyà  acted as mediator between Chà Âshà « Domain and the shogunate. This was regarded by some members of Chà Âshà « (such as Takasugi Shinsaku) as a betrayal. However, during the Boshin War, the domain fought against the shogunate and contributed to the Meiji restoration.
On March 13, 1868, after the Taisei Hà Âkan, the Iwakuni Domain was officially recognized as an independent domain by the new Meiji government. Kikkawa Tsunemoto was recognized as an official daimyà Â. On July 14, 1871 Iwakuni Domain became "Iwakuni Prefecture" due to the abolition of the han system, and was subsequently incorporated into Yamaguchi Prefecture on November 15 of the same year. The Kikkawa family was granted the rank of shishaku (viscount) in the kazoku peerage in 1884.
As with most domains in the han system, Iwakuni Domain consisted of several discontinuous territories calculated to provide the assigned kokudaka, based on periodic cadastral surveys and projected agricultural yields, g.