Ko Samet is one of the eastern seaboard islands of Thailand. It is in the Gulf of Thailand off the coastline of the Thai province of Rayong, approximately 220 kilometres southeast of Bangkok. Ko Samet is part of the Phe Subdistrict of the Amphoe Mueang Rayong, of Rayong Province. Ko Samet is the largest and westernmost of a cluster of islands not far from the coast. Ko Samet measures 6.8 kilometres from north to south.