- JONES, WILLIAM ELWYN EDWARDS (1904 - 1989), Labour politician
- JONES, WILLIAM GARMON (1884 - 1937), professor of history and librarian of Liverpool University
- JONES, WILLIAM HENRY (1860 - 1932), journalist and local historian
- JONES, WILLIAM JENKYN (1852 - 1925) Brittany, Calvinistic Methodist missionary
- JONES, WILLIAM LEWIS (1866 - 1922), professor of English
- JONES, WILLIAM OWEN (1861 - 1937), minister of the 'Free Church of the Welsh', Liverpool
- JONES, WILLIAM OWEN (Eos y Gogledd; 1868 - 1928), musician
- JONES, WILLIAM PHILIP (1878 - 1955), minister (Presb.) and Principal of Trefeca College
- JONES, WILLIAM RICHARD (Goleufryn; 1840 - 1898), Calvinistic Methodist minister, and writer
- JONES, WILLIAM SAMUEL (Wil Sam; 1920 - 2007), playwright
- JONES, WILLIAM TUDOR (1865 - 1946), minister (U) and philosopher
- JONES-DAVIES, HENRY (1870 - 1955), farmer and pioneer of agricultural co-operation
- JONES-DAVIES, THOMAS ELLIS (1906 - 1960), doctor and international rugby player
- JONES-PARRY, Madryn Llyn - see PARRY
- JONES-PIERCE, THOMAS - see PIERCE, THOMAS JONES
- JOSEFF Y SEINAD - see JONES, THOMAS
- JOSHUA, FRANCIS JAMES (1861 - 1920), minister - see JOSHUA, SETH
- JOSHUA, FRANK (1861 - 1920), minister - see JOSHUA, SETH
- JOSHUA, SETH (1858 - 1925), minister (Presb.)
- JOYCE, GILBERT CUNNINGHAM (1866 - 1942), bishop
- MARO, JUDITH - see GROSSMAN, YEHUDIT ANASTASIA
- JUSTINIAN SAINT (fl. 6th century)