Saga Prefecture is a prefecture of Japan located on the island of Kyushu. Saga Prefecture has a population of 809,248 and has a geographic area of 2,440 km2. Saga Prefecture borders Fukuoka Prefecture to the northeast and Nagasaki Prefecture to the southwest.

Kyūshū is the third-largest island of Japan's four main islands and the most southerly of the four largest islands. In the past, it has been known as Kyūkoku , Chinzei and Tsukushi-no-shima . The historical regional name Saikaidō referred to Kyushu and its surrounding islands. Kyushu has a land area of 36,782 square kilometres (14,202 sq mi) and a population of 14,311,224 in 2018.