 18, area ), and a few uninhabited islets, total area .The province of Hydra () was one of the provinces of the Argolis and Corinthia prefecture from 1833 to 1942, Attica prefecture from 1942 to 1964, Piraeus prefecture from 1964 to 1972 and then back to Attica as part of the newly establishment Piraeus prefecture of Attica prefecture.Its territory corresponded with that of the current municipality.