US Post Office—Williamstown Main is a historic post office at 56 Spring Street in Williamstown, Massachusetts. It was built by the federal government in 1932, after the local post office had occupied numerous other commercial spaces in town. The building was designed by James Wetmore and built by the New England General Contractors Company. The rectangular Neo-Classical building is made of Flemish bond brick on a granite foundation, and with marble detailing. Granite steps with wrought iron railings lead up to the main entrance. In the lobby the floor is tiled quarry marble with marble strip details. The walls have a marble panel wainscoting that is topped by plaster. The principal modern intrusions are a glass and aluminum vestibule, and a handicap access ramp.