Leonard Elmhirst was born into a landed gentry family in Worsbrough (now part of Barnsley, Yorkshire), where the family seat is Houndhill. He was the second of nine siblings (eight boys and one girl). His elder brother, Captain William Elmhirst, was killed on 13 November 1916, aged 24, while serving with the 8th Bn. East Yorkshire Regiment during the Battle of the Somme, and the third son, Second Lieutenant Ernest Christopher Elmhirst, was killed on 7 August 1915, aged 20, while serving with the 8th Bn. Duke of Wellington's (West Riding Regiment) during the Gallipoli Campaign; both during World War I. The fourth son, Thomas became Air Marshal Sir Thomas Elmhirst (KBE, CB, AFC, DL, RAF).