island in northern Kalimantan Timur provinsi (East Kalimantan province), northern Indonesia. It is situated in the eastern Celebes Sea, off the northeastern coast of Borneo. The island has a length of approximately 10 miles (16 km) and an area of 117 square miles (303 square km). Its coastal area is low and swampy, and there are oil fields on the southwestern coast. During World War II the island was captured (January 1942) by the Japanese and was retaken by the Australians in May 1945. The town of Tarakan lies on the western side of the island.