The 678th Air Defense Group is a disbanded United States Air Force organization. Its last assignment was with the 20th Air Division of Air Defense Command (ADC) at Tyndall Air Force Base, Florida. The group was formed in 1970 when ADC expanded its radar units that operated Backup Interceptor Control sites from squadron sized units. From 1977 until it was inactivated in 1983 the 678th was responsible for operating the Southern Air Defense System.