- WILLIAMS, HENRY (1624 - 1684), Puritan preacher, prominent as a free-communion Baptist
- WILLIAMS, HENRY PARRY - see PARRY-WILLIAMS, HENRY
- WILLIAMS, HUGH (Hywel Cernyw; 1843 - 1937), Baptist minister, writer, and poet
- WILLIAMS, HUGH (1796 - 1874), solicitor and political agitator
- WILLIAMS, HUGH (1843 - 1911), Calvinistic Methodist minister, and church historian
- WILLIAMS, HUGH (1722? - 1779), cleric and author
- WILLIAMS, HUGH (Cadfan; 1807? - 1870), printer and journalist
- WILLIAMS, Sir HUGH (1718 - 1794), soldier and Member of Parliament
- WILLIAMS, HUGH (1862 - 1953), minister (Presb.), and Biblical commentator
- WILLIAMS, HUGH (1596 - 1670), rector - see WYNN
- WILLIAMS, HUGH (1596 - 1670), rector - see WILLIAMS, Sir WILLIAM
- WILLIAMS, HUGH DOUGLAS (Brithdir; 1917 - 1969), teacher and artist
- WILLIAMS, HUW OWEN (Huw Menai; 1886 - 1961), poet
- WILLIAMS, IESTYN RHYS (1892 - 1955), Director General Labour Relations Department, National Coal Board
- WILLIAMS, Sir IFOR (1881 - 1965), Welsh scholar
- WILLIAMS, IOAN PENRY BRYCHAN ROBERTSON (fl. 1929), author - see WILLIAMS, ALICE MATILDA LANGLAND
- WILLIAMS, IOLO ANEURIN (1890 - 1962), journalist, author and art historian
- WILLIAMS, ISAAC (1802 - 1865), cleric, poet, and theologian
- WILLIAMS, ISAAC JOHN (1874 - 1939), museum official
- WILLIAMS, JAC LEWIS (1918 - 1977), educationalist, author
- WILLIAMS, JAMES (1812 - 1893) Brittany, Calvinistic Methodist missionary
- WILLIAMS, JAMES (1790 - 1872), cleric
- WILLIAMS, JANE (Ysgafell; 1806 - 1885), Welsh historian and miscellaneous writer
- WILLIAMS, JOHN, goldsmith
- WILLIAMS, JOHN (1582 - 1650), dean of Westminster, lord keeper of the great seal, archbishop of York
- WILLIAMS, JOHN (1627 - 1673), Nonconformist preacher, and physician
- WILLIAMS, JOHN (Glanmor; 1811 - 1891), cleric, poet, and antiquary
- WILLIAMS, JOHN (1854 - 1921), Calvinistic Methodist minister
- WILLIAMS, JOHN (d. 1613), principal of Jesus College, Oxford
- WILLIAMS, JOHN (1762 - 1823), Methodist preacher and hymn-writer
- WILLIAMS, JOHN (Ab Ithel; 1811 - 1862), cleric and antiquary
- WILLIAMS, JOHN (1792 - 1858), cleric, scholar, and schoolmaster
- WILLIAMS, JOHN (1806 - 1856), Baptist minister and author
- WILLIAMS, JOHN (1762 - 1802), Evangelical cleric
- WILLIAMS, JOHN (Ioan ap Ioan; 1800 - 1871), Baptist minister and author
- WILLIAMS, JOHN (1760 - 1826), cleric and schoolmaster
- WILLIAMS, JOHN (1801 - 1859), physician and naturalist
- WILLIAMS, JOHN (1768 - 1825), Baptist minister
- WILLIAMS, JOHN (Ioan Madog; 1812 - 1878), blacksmith and poet
- WILLIAMS, JOHN (1745/6 - 1818), cleric and schoolmaster
- WILLIAMS, JOHN (1727 - 1798), Dissenting minister, scholar and author
- WILLIAMS, JOHN (Ioan Rhagfyr; 1740 - 1821), musician
- WILLIAMS, JOHN (1728 - 1806), hymn-writer
- WILLIAMS, JOHN (Siôn Singer; c. 1750 - 1807), musician and Baptist minister
- WILLIAMS, JOHN (1757 - 1810), barrister
- WILLIAMS, JOHN (1754 - 1828), Methodist cleric
- WILLIAMS, JOHN (fl. 1739-1779), Methodist exhorter and hymn-writer
- WILLIAMS, JOHN (1747 - 1831), Methodist cleric
- WILLIAMS, Sir JOHN (1840 - 1926), baronet, Court physician, principal founder of the National Library of Wales
- WILLIAMS, JOHN (Ioan Mai; 1823 - 1887), poet