During the Muromachi period, the area of Akō District was under the control of the Akamatsu clan, the shugo of Harima Province. In the Sengoku period, it was part of the holdings of Ukita Hideie. During the Battle of Sekigahara, Ukita Hideie sided with the losing Western Army, and his territories were confiscated by the victorious Tokugawa Ieyasu, who awarded the area to his general and son-in-law Ikeda Terumasa. His vast holdings were broken up after his death, and his fifth son, Ikeda Masatsuna received a 35,000 koku portion which had been assigned as the widow's portion to his mother Tokuhime. This marked the start of Akō Domain. His younger brother, Ikeda Teruoki, inherited the domain in 1631. However, he went insane in 1645, murdering his concubine and several ladies-in-waiting, and was dispossessed.
The domain was awarded to Asano Naganao, formerly of Kasama Domain in Hitachi Province. Nagaoki spend 13 years building Akō Castle on a scale far in excess of his kokudaka of 53,000 koku and also reconstructed the castle town. In order to alleviate the financial situation, he expanded on coastal salt production (which had been a speciality of the area since the Yayoi period to support the clan's finances. The third daimyō, Asano Naganori was assigned to provide security for the 1682 Joseon missions to Japan and also had to handle a judicial case involving the assassination of TairōHotta Masatoshi by Inaba Masayasu. However, he is more famously known for being one the principal participants in the famous 1702 Akō Incident, in which he was forced to commit seppuku after attempting to kill a powerful shogunal named Kira Yoshinaka and was subsequently avenged by his now masterless retainers.
The Asano clan was replaced at Akō Domain by Nagai Naohiro, formerly of Karasuyama Domain in Shimotsuke Province. However, five years later, in 1706, he was transferred to Iiyama Domain in Shinano Province. The domain was then given to Mori Naganao, who had been daimyō of a 20,000 koku sub-domain of Tsuyama Domain called "Nishiebara Domain". The Mori clan ruled Akō for 165 years until the end of the Edo period. During the Bakumatsu period, pro-Sonnō jōi samurai murdered the domain's karō in front of the gate of Akō Castle in 1861. The revolt was suppressed and seven of the 13 perpetrators were executed. In 1871, with the abolition of the han system, Akō Domain became Akō Prefecture, and was incorporated into Hyōgo prefecture via Shikama Prefecture. The Mori family became a viscount (shishaku) in the kazoku peerage system in 1884.
Holdings at the end of the Edo period
As with most domains in the han system, Ako Domain consisted of several discontinuous territories calculated to provide the assigned kokudaka, based on periodic cadastral surveys and projected agricultural yields.[4][5]
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