Cochin China, region of Indochina, comprising the Mekong delta area of southern Vietnam, bordered by Cambodia, the Gulf of Thailand, and the South China Sea. The principal cities are Ho Chi Minh City (formerly Saigon), Cân Thỏ, Biên Hòa, and My Tho.

From about ad 200 Cochin China was part of the kingdom of Champa, and it was later ruled by the Khmer kingdoms of Cambodia until conquered by the Annamese from the 17th to the 18th century. In 1787 the claimant to the throne of Annam, who then ruled only Cochin China, made a treaty with the French, under which they assisted him in conquering Annam and Tonkin; this was completed in 1802. Subsequent French encroachment, however, led to their taking Saigon in 1859, and by 1867 they had annexed all Cochin China. The Japanese occupied the region in World War II, after which it was briefly made an autonomous republic (1946-1949) and then united with Vietnam (1949-1954). All that time, however, French hegemony was paramount. When Vietnam was divided in 1954, Cochin China became the main part of South Vietnam. It was reabsorbed into the united Socialist Republic of Vietnam in 1975.