In 1864 during the Overland Campaign, Terrill's brother James, by then commanding a brigade, was killed in action at the Battle of Bethesda Church and buried on the battlefield. He was posthumously promoted to brigadier general. Another younger brother, Philip Mallory Terrill of the 12th Virginia Cavalry, was killed near Winchester, Virginia, in November 1864. The fourth brother, Dr. George P. Terrill, a Confederate militia commander, survived the Civil War. An unscrupulous war correspondent from "Harper's Weekly" manufactured a fitting legend that their grieving father later erected a memorial stone for both brothers, which reads "This monument erected by their father. God alone knows which was right."