- SPARK, THOMAS (1655 - 1692), cleric and classical scholar
- SPARKS, JOHN (1726 - 1769), early Moravian
- SPEED, GARY ANDREW (1969 - 2011), footballer
- SPINETTI, VITTORIO GIORGIO ANDRE (1929 - 2012), actor, director and author
- SPINTHER - see JAMES, JOHN SPINTHER
- SPOONER, JAMES (1789 - 1856), railway engineer
- SPURRELL family, printers
- SQUIRES, DOROTHY (1915 - 1998), popular singer
- ST. DAVIDS, 1st Viscount - see PHILIPPS, JOHN WYNFORD
- STANLEY family Penrhos,
- STANLEY, HENRY EDWARD JOHN (3rd Baron Stanley of Alderley and 2nd Baron Eddisbury), (1827 - 1903), Diplomat, translator and writer, hereditary peer
- STANLEY, Sir HENRY MORTON (1841 - 1904), explorer, administrator, and author
- STANLEY, MARGARET, heiress - see WYNN
- STANTON, CHARLES BUTT (1873 - 1946), M.P.
- STAPLEDON, Sir REGINALD GEORGE (1882 - 1960), agricultural scientist
- STEEGMAN, JOHN EDWARD HORATIO (1899 - 1966), author of books on art and architecture
- STENNETT, ENRICO ALPHONSO (1926 - 2011), race relations activist, businessman, dancer
- STENNETT, STANLEY LLEWELLYN (1925 - 2013), musician, comedian, actor
- STEPHAN - see DAVIES, STEPHEN
- STEPHEN, DAVID RHYS (Gwyddonwyson; 1807 - 1852), Baptist minister and author
- STEPHEN, DOUGLAS CLARK (1894 - 1960), newspaper editor
- STEPHEN, EDWARD (JONES) (Tanymarian; 1822 - 1885), musician
- STEPHEN, ROBERT (1878 - 1966), schoolmaster, historian and poet
- STEPHEN, THOMAS (1856 - 1906), musician
- STEPHENS, JOHN OLIVER (1880 - 1957), Independent minister and professor at the Presbyterian College, Carmarthen
- STEPHENS, MEIC - see STEPHENS, MICHAEL
- STEPHENS, MICHAEL (1938 - 2018), writer and literature administrator
- STEPHENS, THOMAS (Casnodyn, Gwrnerth, Caradawg; 1821 - 1875), historian and social reformer
- STEPHENS, THOMAS (1821 - 1875)
- STEPHENSON, THOMAS ALAN (1898 - 1961), zoologist
- STEPNETH, Prendergast - see STEPNEY
- STEPNEY family Prendergast,
- STINAN Saint - see JUSTINIAN, Saint
- STONE, TIMOTHY - see ELLIS, THOMAS IORWERTH
- STONELAKE, EDMUND WILLIAM (1873 - 1960), politician and a key figure in establishing the Labour Party in the Merthyr Boroughs constituency
- STOW HILL of NEWPORT, Baron - see SOSKICE, FRANK
- STRACHAN, GILBERT INNES (1888 - 1963), professor of medicine
- STRADLING family
- STRICKLAND, ANN (d. 1687), landowner - see MORGAN, Sir CHARLES
- SULGENUS - see SULIEN
- SULIEN (1011 - 1091), teacher and Bishop of St David's
- SULLIVAN, CLIVE (1943 - 1985), rugby league player
- SUNDERLAND, ERIC (1930 - 2010), academic
- SUTTON, Sir OLIVER GRAHAM (1903 - 1977), meteorologist
- SWANSEA, 1st Baron - see VIVIAN, HENRY HUSSEY
- SYMMONS family Llanstinan,
- SYMONDS, RICHARD (1609 - ?), Puritan preacher
- SYPYN CYFEILIOG (fl. 1340-1390), poet
- SYPYN CYFEILIOG - see CNEPPYN GWERTHRYNION