Ios is a Greek island located within the Cyclades group in the Aegean Sea. It is situated approximately halfway between the islands of Naxos and Santorini. Administratively, the island is part of the Thira regional unit.
The island measures roughly 18 kilometres in length and 10 kilometres in width, covering a total area of 109.024 square kilometres (42.094 sq mi). Its geography is characterized by hilly terrain with cliffs that descend steeply into the sea on most sides. As of the 2021 census, Ios had a population of 2,299 residents.