The island took its name from Kythnos, the leader of the tribes Driopes who came from Evia island, Greece. The four graves that were excavated in the region Maroulas, close to Loutra village, are the oldest samples of human presence in the Aegean, testifying that the island was inhabited from the Mesolithic Era, between 9500-8500 BC.
As shown by historical remarks, the inhabitants of Kythnos took part in the Persian Wars, while in the Medieval era, the island was conquered by Romans and Franks. The locals also took part in the Greek Revolution of 1821. Historical resources mention that one fourth of the local population died in 1823 due to plague.
An important landmark in the history of Kythnos was the German occupation (1941-1945) during World War II, when life on the island was very difficult, as was in the rest of Greece. However, the capitulation of Italy in 1943 marked the starting point for active resistance by the locals, a resistance that was also official acknowledged by the Greek State.