Bill Cowsill was born in Middletown, Rhode Island, the eldest child of the seven Cowsill children—six boys and one girl—and was named after his father, William "Bud" Joseph Cowsill Sr. (1925–1992). At a young age, Bill began singing with his younger brother, Bob (born August 26, 1949), playing guitars provided for them by their father, Bud, then serving in the U.S. Navy. The brothers had originally wanted to form a rock band. At their father's insistence, Bill and Bob Cowsill formed The Cowsills in 1965 with their brothers Barry on bass and John on drums. Their father became their full-time manager, following his retirement from the Navy. He was physically and emotionally abusive towards his family, in both his spousal and parental roles. Such abuse continued during his role as the group's manager.