Koga Domain

Koga Domain (古河藩, Koga-han^?) was a feudal domain under the Tokugawa shogunate of Edo period Japan. It is located in Shimōsa Province, Honshū. The domain was centered at Koga Castle, located in what is the city of Koga in Ibaraki Prefecture.

During the Muromachi period, Koga was the seat of the Kantō kubō, under the Ashikaga clan, who vied with the Uesugi clan and with the Late Hōjō clan for control of eastern Japan.

When Toyotomi Hideyoshi defeated the Hōjō at the Siege of Odawara, the area fell into his hands, and was subsequently assigned (along with the rest of the Kantō region) to Tokugawa Ieyasu. Ieyasu assigned Koga Castle to his grandson-in-law, Ogasawara Hidemasa as daimyō of Koga Domain, with assessed kokudaka of 30,000 koku.

Afterwards, the domain was reassigned every couple of generations to a large number of fudai daimyō clans, spending the longest time under the control of the Doi clan (1633–1681, 1762–1871).

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