Kastos is a Greek island and a former community east of the island of Lefkada, Ionian Islands, Greece. Since the 2011 local government reform it is part of the municipality Lefkada, of which it is a municipal unit. Until 1974, when it became part of the Lefkada Prefecture, the island was administered under the Cephalonia Prefecture (Ithaca province). The nearest island is Kalamos, with a deep channel between them; the mainland is approximately to the northeast in Aetolia-Acarnania.