William Thayer may refer to:
William Greenough Thayer (1863–1934), American educator
W. Paul Thayer (1919–2010), American test pilot, aviation executive, and Deputy Secretary of Defense during the Reagan Administration William Roscoe Thayer (1859–1923), American author and editor William Sydney Thayer (consul) (died 1864), American Consul General to Egypt (1861–1864) - see United States Ambassador to Egypt William Sydney Thayer (1864–1932), American physician and professor of medicine W. W. Thayer (William Wallace Thayer, 1827–1899), American politician, governor of Oregon, and Oregon Supreme Court chief justice William Wilde Thayer, one of the founders of the short-lived Thayer & Eldridge publishing firm (c. 1860–1861) William Thayer Arteaga (1918–2018), Chilean politician