John Spencer, 1st Earl Spencer (1734-1783) was the son of Hon. John Spencer and Lady Georgiana Caroline Carteret. He married Margaret Georgiana Poyntz, daughter of Rt. Hon. Stephen Poyntz and Anne Maria Mordaunt, on 20 December 1755 at Althorp, Brington, Northamptonshire, England.
He was created 1st Viscount Spencer of Althorp and 1st Baron Spencer of Althorp [GB] on 3 April 1761, and 1st Earl Spencer and 1st Viscount Althorp [GB] on 1 November 1765.
Children of John Spencer, 1st Earl Spencer and Margaret Georgiana Poyntz
Lady Georgiana Spencer b. 7 Jun 1757, d. 30 Mar 1806
George John Spencer, 2nd Earl Spencer b. 1 Sep 1758, d. 10 Nov 1834
Lady Henrietta Frances Spencer b. 16 Jun 1761, d. 11 Nov 1821
Lady Charlotte Spencer b. 1765, d. 1766
Lady Louisa Spencer b. 1769, d. 1769
Richard Milward, ‘Spencer, John, first Earl Spencer (1734–1783)’, Oxford Dictionary of National Biography, Oxford University Press, 2004 accessed 17 Aug 2017. This is a subscription site but access is free to readers of British libraries whose library subscribes.