William Dewey Foster (1890 – 1958) was an American architect.
Foster received his training from the Massachusetts Institute of Technology. During the 1910s and 1920s, he worked as a draftsman for a number of architectural firms before going into private practice. In 1934 he, along with 20 other architects, were hired on a consultatory basis by the Office of the Supervising Architect to help with the increased workload of New Deal projects. During his eight-year tenure with the Office he designed a number of post office buildings located in the New York City area. He also designed the Weather Bureau (1940) and State Department (1942) offices.