- WILLIAMS, JOHN (Gorfyniawc o Arfon; 1814 - 1878), musician
- WILLIAMS, JOHN (1833 - 1872), antiquary and lawyer
- WILLIAMS, JOHN (1825 - 1904), cleric and author
- WILLIAMS, JOHN (RUFUS) (Rufus; 1833 - 1877), Baptist minister and author
- WILLIAMS, JOHN (1856 - 1917), teacher of singing and choral conductor
- WILLIAMS, JOHN (J.W. Llundain; 1872 - 1944), slate merchant
- WILLIAMS, JOHN - see PRICHARD, JOHN WILLIAM
- WILLIAMS, JOHN (1700 - 1787), chief justice of Brecknock - see WILLIAMS, Sir WILLIAM
- WILLIAMS, JOHN (1784 - 1876), barrister - see WILLIAMS, JAMES
- WILLIAMS, JOHN (d. 1738), attorney-general - see WILLIAMS, Sir WILLIAM
- WILLIAMS, JOHN CEULANYDD (Ceulanydd; 1847? - 1899), Baptist minister, poet, and writer
- WILLIAMS, JOHN ELLIS (1901 - 1975), author and dramatist
- WILLIAMS, JOHN ELLIS CAERWYN (1912 - 1999), Welsh and Celtic scholar
- WILLIAMS, JOHN HUW (1871 - 1944), newspaper editor
- WILLIAMS, JOHN JAMES (1869 - 1954), minister (Congl.) and poet
- WILLIAMS, JOHN JOHN (1884 - 1950), school-teacher, education administrator, producer and drama adjudicator
- WILLIAMS, Sir JOHN KYFFIN (1918 - 2006), painter and author
- WILLIAMS, JOHN LEWIS (1882 - 1916), Wales and Cardiff Rugby wing three-quarter, and coal exporter (Greenslade and Williams)
- WILLIAMS, Sir JOHN LIAS CECIL CECIL- - see CECIL-WILLIAMS, Sir JOHN LIAS CECIL
- WILLIAMS, JOHN LLOYD (1854 - 1945), botanist and musician
- WILLIAMS, JOHN OWEN (Pedrog; 1853 - 1932), Congregational minister, and poet
- WILLIAMS, JOHN RICHARD (J.R. Tryfanwy; 1867 - 1924), poet
- WILLIAMS, Baron Williams of Thame JOHN (1500? - 1569), custodian of the crown jewels of Henry VIII - see WILLIAMS, JOHN
- WILLIAMS, JONATHAN (1752? - 1829), cleric, schoolmaster, and antiquary
- WILLIAMS, KATE - see ROBERTS, CATHERINE
- WILLIAMS, LAURA EVANS- - see EVANS-WILLIAMS, LAURA
- WILLIAMS, LEWIS - see WILLIAM, LEWIS
- WILLIAMS, LLEWELLIN (1725 - ?), sailor and painter
- WILLIAMS, LLEWELLYN (1822 - 1872), harpist - see WILLIAMS, ZEPHANIAH
- WILLIAMS, LLYWELYN (1911 - 1965), minister (Congl.) and politician
- WILLIAMS, LUCY GWENDOLEN (1870 - 1955), sculptress
- WILLIAMS, MALLT - see WILLIAMS, ALICE MATILDA LANGLAND
- WILLIAMS, MARGARET LINDSAY (1888 - 1960), artist
- WILLIAMS, MARGARETTA (Rita) (1933 - 2018), lecturer and Celtic linguist
- WILLIAMS, MARIA JANE (Llinos; 1795 - 1873), folklore collector and musician
- WILLIAMS, MARIA JANE (Llinos; 1795? - 1873), musician
- WILLIAMS, MARY (1883 - 1977), French scholar
- WILLIAMS, MATHEW (1732 - 1819), landsurveyor, author, and almanack-maker?
- WILLIAMS, MATTHEW (d. 1801), actor
- WILLIAMS, MEIRION (1901 - 1976), musician
- WILLIAMS, MORGAN (1808 - 1883), chartist
- WILLIAMS, MORGAN (c. 1750 - 1830), cleric
- WILLIAMS, MORGAN, Dissenting layman - see WILLIAMS, ROGER
- WILLIAMS, MORRIS (Nicander; 1809 - 1874), cleric and man of letters
- WILLIAMS, MOSES (1685 - 1742), cleric and scholar
- WILLIAMS, MOSES (d. 1819), General (but Trinitarian) Baptist minister, and blacksmith
- WILLIAMS, NATHANIEL (1742 - 1826), Baptist (Particular, afterwards General) minister, theological controversialist, hymn-writer, and amateur doctor
- WILLIAMS, NATHANIEL (1656/7 - c. 1679), author
- WILLIAMS, ORIG (1931 - 2009), footballer, wrestler, promoter and journalist
- WILLIAMS, OWEN (Owain Gwyrfai; 1790 - 1874), antiquary