Through his paternal lineage, MacCormac was the great-grandson of Dr. Henry MacCormac, a prominent nineteenth-century physician in Northern Ireland who was the father of Sir William MacCormac, 1st Bt, KCB, KCVO, who served as a house physician and surgeon to Queen Victoria and honorary sergeant-surgeon to King Edward VII. The family was a well-known medical dynasty in the nineteenth century that originated from County Armagh and claims descent from Cornelius MacCormac, a high-ranking naval officer, and Colonel Joseph Hall, a wealthy distiller in County Armagh. Distant relatives also include a branch of the Easmon family of Sierra Leone, descended from Dr. John Farrell Easmon, the discoverer of Blackwater fever.
