Mattapan (/mætəˈpæn/) is a neighborhood in Boston, Massachusetts. Historically a section of neighboring Dorchester, Mattapan became a part of Boston when Dorchester was annexed in 1870. As of the 2010 census, it had a population of 36,480. Like other neighborhoods of the late 19th and early 20th century, Mattapan developed, residentially and commercially, as the railroads and streetcars made downtown Boston increasingly accessible.