Trefusis (variants Trefusa and Trefuse) is a Cornish surname derived from the hamlet of Trefusis in the parish of Mylor, Cornwall. Among bearers of the name are the Barons Clinton: that title was successfully claimed in 1794 by Robert George William Trefusis, who became the seventeenth Baron.
The arms of Trefusis are: Argent a chevron between three spindles Sable; and the crest: A griffin segreant Or resting his dexter foot on a shield Argent.
- Charles Trefusis, 19th Baron Clinton (1791–1866), a British peer and Tory politician.
- Francis Trefusis, one of the MPs for Penryn in 1679 and has a monument in Mylor church, dated 1680.
- John Trefusis of Trefusis was High Sheriff of Cornwall in 1626.
- Mark George Kerr Trefusis (1835–1907), later Mark George Kerr Trefusis Rolle - large Devonshire landholder, High Sheriff of Devonshire
- Nicholas Trefusis (d. c1648),English politician who sat in the House of Commons of England
- Robert Trefusis (1843–1930), Inaugural Suffragan Bishop of Crediton from 1897 to 1930
- Violet Trefusis (1894–1972), English writer and socialite
- Miss Emily Trefusis, amateur detective in The Sittaford Mystery by Agatha Christie
- Professor Donald Trefusis (1921–2008), Professor at the University of Cambridge
- Dr.Trefusis, tutor in "Octavian Nothing" volumes 1&2 by M.T. Anderson
- Pascoe, W. H. (1979) A Cornish Armory. Padstow: Lodenek Press; p. 104
- Pevsner, N. (1969) Cornwall; 2nd ed. Harmondsworth: Penguin; p. 125
- "In the chancel aisle kneels a young man born when Charles Stuart was about to die ; he is Francis Trefusis, carved in stone."--Arthur Mee in his Cornwall; England's farthest south, London: Hodder & Stoughton, 1937.
- Polwhele, Richard (1806) The Civil and Military History of Cornwall. London: Cadell and Davies; vol. 1, pp. 106-09