Chumphon is one of the southern provinces of Thailand, at the shore of the Gulf of Thailand. Neighboring provinces are (from north clockwise) Prachuap Khiri Khan, Surat Thani and Ranong. To the west it also borders Myanmar.
Chumphon is located on the Isthmus of Kra, the narrow landbridge connecting the Malay Peninsula with the mainland of Thailand. To the west are the hills of the Phuket mountain range and its northern continuation, the Tenasserim chain, while the east is the more flat land at the coat to the Gulf of Thailand. The main river is the Lang Suan, which originates in Phato district.