Serifos is a Greek island municipality in the Aegean Sea, located in the western Cyclades, south of Kythnos and northwest of Sifnos. It is part of the Milos regional unit. The area is 75.207 square kilometres and the population was 1,241 at the 2021 census. It is located about 170 kilometres ESE of the Athenian port of Piraeus.