Cacavas was born in Aberdeen, South Dakota in 1930. His father was an emigrant from Greece and his mother was born in North Dakota. He had a fraternal twin sister, Jeanne, and numerous other siblings: Peter David, b. 1928; Penelope, b. 1932; and Adrian G., 1933. Their father's younger brother Chris had also immigrated to South Dakota and lived in Aberdeen, where he married and had a family. John and his siblings attended local schools; he displayed an early talent for music, forming a local band at age 14, at 16 he started a school dance band named “The Golden Blues," he left after having a falling out with his band teacher after which he quit all school band activities. He studied musical composition at Northwestern University.
