Karatsu Domain, located in Hizen Province, was a prominent feudal domain that held authority over the region. The ruling family's residence, known as Karatsu Castle, was situated in Karatsu City, Saga Prefecture. As the seat of power, Karatsu Castle served as a symbol of the domain's influence and played a crucial role in governing the surrounding territories. The domain's rule over Karatsu and its strategic location in Hizen Province contributed to its significance in the feudal era.

Hizen Province was an old province of Japan in the area of the Saga and Nagasaki prefectures. It was sometimes called Hishū (肥州), with Higo Province. Hizen bordered on the provinces of Chikuzen and Chikugo. The province was included in Saikaidō. It did not include the regions of Tsushima and Iki that are now part of modern Nagasaki Prefecture.