William Allen may refer to:
Politicians
United States
William Allen (congressman) (1827–1881), United States Representative from Ohio
William Allen (governor) (1803–1879), U.S. Representative, Senator, and 31st Governor of Ohio William Allen (loyalist) (1704–1780), wealthy merchant, chief justice of Pennsylvania's provincial Supreme Court, and founder of Allentown, Pennsylvania William Allen (Montana politician) (1871–1953), member of the Montana House of Representatives and lieutenant governor William C. Allen (politician) (1814–1887), American businessman and politician in Wisconsin William F. Allen (Delaware politician) (1883–1946), American businessman and politician William F. Allen (New York politician) (1808–1878), American judge and politician William Fessenden Allen (1831–1906), American businessman and royal advisor in the Kingdom of Hawaii William H. Allen (politician), member of the Mississippi House of Representatives in the 1880s William J. Allen (1829–1901), congressman from Illinois and federal judge William P. Allen (politician) (1818–1901), member of the Wisconsin State Assembly William Reynolds Allen (1860–1921), justice of the North Carolina Supreme Court William S. Allen (1857–1926), Iowa Secretary of State, 1913–1918 William V. Allen (1847–1924), U.S. Senator from Nebraska William W. Allen (politician) (1908–1992), member of the Pennsylvania House of Representatives William Allen (Massachusetts judge) (died 1891), Justice of the Massachusetts Supreme Judicial Court
Other
William Allen (National Liberal politician) (1870–1945), British politician
William Allen (Armagh MP) (1866–1947), Northern Irish unionist politician
William Allen (Canadian politician) (1919–1985), from Toronto
William Bell Allen (1812–1869), Australian politician from New South Wales
William Edward David Allen (1901–1973), British politician and historian
William Johnston Allen (1835–1915), Australian politician from New South Wales
William Shepherd Allen (1831–1915), English Liberal politician
Artists, architects, writers, and scholars
William Allen (actor) (died 1647), English actor in the Caroline era
William Allen (biographer) (1784–1868), American evangelical Congregationalist
William Allen (Utah architect) (1849–1928), American architect in Utah
William H. Allen (architect) (1858–1936), architect of New Haven, Connecticut
William B. Allen (born 1944), American political scientist
William Francis Allen (1830–1889), American classical scholar
William Henry Allen (academician) (1808–1882), American professor
W. H. Allen (artist) (William Herbert Allen, 1863–1943), English landscape watercolour artist William Rodney Allen, American author and professor of English William Sheridan Allen (1932–2013), American author and historian W. Sidney Allen (1918–2004), English linguist and philologist William T. Allen (1944–2019), professor of corporate law at New York University law school
Military personnel
William Allen (Royal Navy officer) (1792–1864), English naval officer and explorer William Allen (soldier) (1845–1882), American recipient of Medal of Honor William Allen (VC 1879) (1843–1890), English recipient of the Victoria Cross William Barnsley Allen (1892–1933), English recipient of the Victoria Cross William Henry Allen (1784–1813), American naval officer William Howard Allen (1790–1822), American naval officer William W. Allen (general) (1835–1894), Confederate general
Scientists
William Allan (geneticist) (1881–1943), American physician and geneticist
William Allen (English Quaker) (1770–1843), English Quaker, scientist and philanthropist William Douglas Allen (1914–2008), British/Australian physicist and electrical engineer William Henry Allen (engineer), (1844–1926), British engineer
Sports people
William Allen (sailor) (born 1947), American sailor and Olympic champion
William Reginald Allen (English cricketer) (1893–1950), English cricketer
William L. Allen (died 1907), American football player and coach
William D. Allen (1886–1979), American football and basketball coach
Clergy and philanthropists
William Allen (cardinal) (1532–1594), English Roman Catholic cardinal priest
William Allen (English Quaker) (1770–1843), English Quaker, scientist and philanthropist William Allen (Quaker minister) (1821–1898), American Quaker minister, also active in Canada William Allen (philanthropist) (1790–1856), English-Australian philanthropist William Allen (Congregationalist) (1847–1919), English-born, Australian Congregational clergyman