Trizonia is a small island in Corinthian Gulf and the only inhabited island among the islands of the Corinthian gulf. Along with the nearby islets Prasoudi, Planemi and Agios Ioannis comprise a small group of islands. It is located off the north coast of the Corinthian gulf, opposite the villages Glyfada and Chania of Phocis prefecture. Its area is 2.5 square kilometers and its population is 55 inhabitants according to 2021 census.