I Corps (Vietnamese: Quân đoàn I) was a corps of the Army of the Republic of Vietnam (ARVN), the army of the nation state of South Vietnam that existed from 1955 to 1975. It was one of four corps of the ARVN. This was the northernmost region of South Vietnam, bordering North Vietnam at the Vietnamese Demilitarized Zone (DMZ). These five provinces are Quảng Trị Province, (Khe Sanh, Đông Hà, Quảng Trị City), Thừa Thiên-Huế Province, (Phu Bai, Huế City), Quảng Nam Province, (Đà Nẵng, Hội An), Quảng Tín Province, (Tam Kỳ, Chu Lai) and Quảng Ngãi Province, (Quảng Ngãi).