William Welles Bosworth (May 8, 1869 – June 3, 1966) was an American architect whose most famous designs include the Massachusetts Institute of Technology Cambridge campus, the original AT&T Building in New York City, and the Theodore N. Vail mansion in Morristown, New Jersey (1916, now the Morristown Town Hall). Bosworth was also responsible to a large degree for the architectural expression of Kykuit, the Rockefeller family estate in Pocantico Hills, New York, working closely with the architects William Adams Delano and Chester H. Aldrich, and the interior designer Ogden Codman.