Ko Samet is one of the Eastern Seaboard Islands of Thailand. It is located in the Gulf of Thailand off the coastline of the Thai province of Rayong, approximately 220 kilometres (140 mi) southeast of Bangkok. Ko Samet is part of the Phe Subdistrict of the Amphoe Mueang Rayong (Thai: เมืองระยอง, the capital district, or Amphoe Mueang), of Rayong province. Ko Samet is the largest and westernmost of a cluster of islands not far from the coast.
The island derives its name from the cajeput tree found throughout the island, as the Thai language word for cajeput is samet (the cajeput tree is formally known in