The library is named for
General Sylvanus Thayer, who helped found it through a $30,000 bequest in his will. The original building was dedicated June 4, 1874, and opened to the public in September of the same year. It operated as a library until 1953, when it was replaced by a larger building across the street. The 1874 building was occupied by the Braintree Water Department for many years, but is currently vacant. This building was listed on the
National Register of Historic Places in 1978. In 1997, the 1953 library building was razed and replaced by the current three-story brick
postmodern building that opened in 1999. ==Antitrust lawsuit participation==