was a feudal domain under the Tokugawa shogunate of Edo period Japan, in what is now part of Shimonoseki, Yamaguchi Prefecture. It was centered around Kushizaki Castle and was ruled throughout its history by a cadet branch of the Mà Âri clan. Chà Âfu Domain was dissolved in the abolition of the han system in 1871. The domain was also called or .
Mà Âri Hidemoto, the grandson of Mà Âri Motonari was adopted by Mà Âri Terumoto in 1592 as Terumoto was concerned about his impending deployment to Korea whilst without an official heir. Mà Âri Motonari agreed to the adoption on the stipulation that if Terumoto should subsequently have a biological heir, his fiefdom would be divided between Hidemoto and the new heir. This in fact occurred with the birth of Mà Âri Hidenari. Toyotomi Hideyoshi recognized Hidenari as Terumoto's successor in 1598. The following year, Hidemoto received a total of 170,000 koku of estates in Nagato Province, Saiki District in Aki Province and Kishiki District in Suà  Province. Although a vassal of Chà Âshà « Domain, Hideyoshi gave him official recognition as an independent daimyà Â.
After the Battle of Sekigahara in 1600, the Mà Âri territory was reduced from 1,120,000 koku to 298,000 koku, and was forced to relocate their seat to Nagato Province. The Kikkawa clan was assigned Iwakuni Domain to protect the eastern approaches, and Mà Âri Hidemoto was given new territory in Toyoura District, Nagato (now part of Shimonoseki) to guard the west. The domain's kokudaka was nominally set at 60,000 koku, but under the 3rd daimyà  Mà Âri Tsunamoto, 10,000 koku was assigned to his uncle, Mà Âri Mototomo, to form Kiyosue Domain, another subsidiary domain of Chà Âshà « Domain in 1653. Mà Âri Tsunamoto's son Mà Âri Yoshimoto and the 8th daimyà Â, Mà Âri Masatake became daimyà  of Chà Âshà « Domain when the direct lineage failed to produce an heir. In 1718, the domain was reduced to 38,000 koku, but increased back to 47,000 koku in 1720 and 50,000 koku in 1783. During the Bakumatsu period, Chà Âfu Domain initially attempted to separate itself from the increasingly restive and radicalized Chà Âshà « Domain and come under direct control of the Tokugawa shogunate, but this attempt was unsuccessful and Chà Âfu subsequently fought in the Boshin War together with Chà Âshà « and the other Chà Âshà « sub-domains. After the Meiji restoration, the domain was briefly (1869-1871) renamed before becoming âÂÂToyoura PrefectureâÂÂ, which was subsequently incorporated into Yamaguchi prefecture.
The final daimyà  of Chà Âfu, Mà Âri Mototoshi was granted the kazoku peerage title of viscount (shishaku). It was often stated that Emperor Meiji refused to grant him the title of count (hakushaku) as Emperor Meiji's uncle, Nakayama Tadamitsu had been assassinated while in exile in Chà Âfu. However, as the kazoku peerage guidelines stipulated that former daimyà  with kokudaka of between 10,000 and 50,000 koku were to become viscounts, this allegation does not hold water.
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.