John Campbell 
1. G.E. Cokayne; with Vicary Gibbs, H.A. Doubleday, Geoffrey H. White, Duncan Warrand and Lord Howard de Walden, editors, The Complete Peerage of England, Scotland, Ireland, Great Britain and the United Kingdom, Extant, Extinct or Dormant, new ed., 13 volumes in 14 (1910-1959; reprint in 6 volumes, Gloucester, U.K.: Alan Sutton Publishing, 2000), volume II, page 512. Hereinafter cited as The Complete Peerage.
2. Charles Mosley, editor, Burke's Peerage and Baronetage, 106th edition, 2 volumes (Crans, Switzerland: Burke's Peerage (Genealogical Books) Ltd, 1999), volume 1, page 103. Hereinafter cited as Burke's Peerage and Baronetage, 106th edition.