Kos, also known as Cos, is a Greek island located in the southeastern Aegean Sea as part of the Dodecanese island chain. It serves as a municipality within the Kos regional unit of the South Aegean region. The island measures approximately 42.1 by 11.5 kilometres.
As the third largest island in the Dodecanese, following Rhodes and Karpathos, Kos has a population of 37,089. This makes it the second most populous island in the chain after Rhodes. The town of Kos serves as the principal town and the seat of the municipality.