William Dennis (1856–1920) was an Independent Conservative member of the Senate of Canada.

• William Henry Dennis (1887–1954), his nephew and Canadian Conservative senator from 1912 to 1920

William or Billy Dennis may also refer to:

• Billy Dennis (English footballer) (1896–1952), English footballer
• Willie Dennis (1926–1965), American jazz musician
• Willie D (born 1966), rapper
• Bill Dennis (born 1935), NASCAR driver
• William Lockyer Dennis (1853–1919), English-born American politician
• William M. Dennis (1810–1882), American businessman and politician
• William S. Dennis (fl. 1910s), American captain of the Vanitie yacht in the America's Cup trials
• Will Dennis (born 2000), English footballer

• All pages with titles beginning with William Dennis