Hammond was born in Washington, D. C. , the son of Colonel Thomas West Hammond, Jr. by his wife Eileen Hammond (née Bennett). While Hammond's father was a US citizen and an officer in the US Army, his mother was an Englishwoman who had played a role in Much Too Shy in 1942. Hammond has one elder brother, David (b. 1946). Hammond's parents had met and married in London during World War II when his father had been posted there. After the war, the couple had moved to the U. S. permanently, and because the Colonel had an army job, the family moved numerous times to various army stations across the country during Hammond's childhood. Col. Hammond died in 1970.