John Alexander Dunnington-Jefferson was born in Bournemouth[1] on 10 April 1884, the eldest son of Captain Mervyn Dunnington-Jefferson (1850–1912), JP, of Thicket Priory and Middlethorpe Hall, Yorkshire, and his wife Louisa Dorothy (died 1951), daughter of the Rev.
[2] The Dunnington family had been landowners in the East Riding from the 17th century and had an estate centred on Thorganby and West Cottingwith.
John Dunnington-Jefferson inherited the family estates from his childless uncle in 1928; in 1955, he sold Thicket Priory to Carmelite nuns and moved to Thorganby Hall but then sold his lands in Thorganby and West Cottingwith in 1964.
He served in Europe during the First World War, earning the Distinguished Service Order (DSO) in 1917 and being mentioned in dispatches six times; he also received the French Legion of Honour, the Belgian War Cross and the Italian Order of St Maurice and St Lazarus.
[4][8] He deposited his family's papers at Hull University Archives in 1974 (reference GB 50 U DDJ).