Serifos (, , also Seriphos; formerly Serpho or Serphanto) 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 and the population was 1,420 at the 2011 census. It is located about ESE of Piraeus. In Greek mythology, Serifos is where Danaë and her infant son Perseus washed ashore after her father Acrisius, in response to an oracle that his own grandson would kill him, set them adrift at sea in a wooden chest. When Perseus returned to Serifos with the head of the Gorgon Medusa, he turned Polydektes, the king of Serifos, and his retainers into stone as punishment for the king's attempt to marry his mother by force.