Ganghwa Island, island, Gyeonggi do (province), northwestern South Korea. Ganghwa Island lies in the Yellow Sea just off the northwestern coast, northwest of Incheon. Roughly rectangular in shape, it lies at the mouth of the Han River and has an area of 163 square miles (422 square km). The land is hilly but fertile and produces rice and other crops; the island is one of the country’s leading areas for ginseng cultivation. The principal towns are Ganghwa, in the northeast, and Dongmak, in the south. The island was temporarily seized by the French in 1866 and by Americans in 1871. Pop. (2020) 66,020.