Politicians

• William Allen (1919–1985), Canadian politician from Toronto
• William Allen (1827–1881), American congressman from Ohio
• William Allen (1803–1879), American politician from Ohio
• William Allen (1866–1947), Northern Irish unionist politician
• William Allen (1870–1945), British politician
• William F. Allen (1883–1946), American businessman and politician

Artists, writers and scholars

• William Allen (1957–), artist
• William Allen (1784–1868), evangelical Congregationalist
• William Francis Allen (1830–1889), American classical scholar
• William Rodney Allen, American author and professor of English
• William Sheridan Allen, American author and historian

Military personnel

• William Henry Allen (1784–1813), naval officer
• William Howard Allen (1790–1822), United States naval officer
• William Allen (1792–1864), English naval officer and explorer
• William Allen (1845–1882), American recipient of Medal of Honor
• William Barnsley Allen (1892–1933), English recipient of Victoria Cross
• William Wilson Allen (ca. 1844–1890), English recipient of the Victoria Cross

Others

• William Allen (1532–1594), English Catholic priest and cardinal
• William Allen (1893–1950), English cricketer
• William Allan (1881–1943), American physician and geneticist
• William Allen (1704–1780), founder of Allentown, Pennsylvania
• William Allen (ca. 1790–1856), English-Australian philanthropist
• William Allen (1770–1843), English Quaker, scientist and philanthropist
• William E. Allen, director of the U.S. Bureau of Investigation
• William Edward David Allen (1901–1973), British politician and historian
• William F. Allen (1808–1878), American judge and comptroller
• William Henry Allen (1808–1882), American professor
• William Joshua Allen (1829-1901), American federal judge
• William McPherson Allen (1900–1985), American aircraft businessman
• William Allen (1829–1875), American landowner and financier from Virginia
• William V. Allen (1847–1924), American jurist and senator from Nebraska

See also

• Bill Allen
• Willie Allen
• Will Allen
• William Allan
• William Allen High School, Allentown, Pennsylvania, U.S.A.
• William Van Alen, U.S. architect