Ko Island (小島, Ko-jima) or Kojima is an uninhabited volcanic island in the Sea of Japan, 23 kilometres (14 mi) southwest of the mainland portion of the town of Matsumae[2] and is the southernmost point in Hokkaidō.

[5] Several smaller islets surround Ko Island, including Daihiyakushima, Shohiyakushima, Tenjinshima, and Sazaeshima.

The island, along with some neighbouring islets, have been recognised as an Important Bird Area (IBA) by BirdLife International because they also support colonies of rhinoceros auklets.

For this reason it is a major fishing area for fishermen out of Matsumae, especially because of the decline in the Arabesque greenling over the last 24 to 25 years.

[2] The predominant vegetation on the island is grasses, but there are stands of Acer pictum subsp.