Covering an area of 2,204.7 square kilometres (851.2 sq mi), it is the fourth-largest island in the country, and the largest off the mainland. The western part of the island is in the Vesterålen district, while the southwestern part is in Lofoten. As of 2006, it had a population of 31,851, of which the only town is Harstad. Villages include Borkenes, Lødingen, Sigerfjord and Sørvik.
The island is split between the municipalities of Harstad and Kvæfjord in Troms, and Andøy, Hadsel, Lødingen, Sortland, Tjeldsund and Vågan in Nordland. Hinnøya is dissected by several fjords, and contains a mostly rugged and mountainous terrain, especially the southern part. The best agricultural area is in the northeast, in Harstad and Kvæfjord. The southern part is the location of Møysalen National Park, which includes the highest mountain on the island, Møysalen, with its 1,262 metres (4,140 ft) above sea level.