Wescomb was born at Langford Grove in 1788 and baptised on 6 June 1788 at St. Giles Church, Langford. He was the son of Nicholas Wescomb (1732–1808) and Lucy (née Marshall) Wescomb (1744–1835). His elder brother was John Emerton Wescomb.
His paternal grandparents were William Wescomb and Elizabeth (née Wotton) Wescomb. His maternal grandparents were William Marshall and Anne (née Gatwood) Marshall.
Lucy Elizabeth Jane Wescomb (1822–1912), who married George Byron, 8th Baron Byron, a son of George Byron, 7th Baron Byron and Elizabeth Mary Chandos-Pole (the daughter of Sacheverell Pole, of Radbourne Hall), in 1843. After his death in 1870, she married her cousin, the Rev. Philip Henry Douglas (a grandson of the Rev. Philip Douglas) in 1878. Douglas was the Vicar at Thrumpton in 1873.
↑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: Alan Sutton Publishing, 2000), vol. II, p. 458.