The City Hall Historic District includes buildings dating back to as far as 1823.  Both Old City Hall (1830, 222 Merrimack Street) and New City Hall (1893, 375 Merrimack Street), can be found in the district along with many commercial, residential, religious, and institutional structures.  It contains examples of all eras of the city's development and is the commercial and governmental center of the city.  Examples of the Federal, Greek Revival, Gothic Revival, Italianate, Second Empire, High Victorian Gothic, Romanesque Revival, Richardsonian Romanesque, and Classical  Revival styles can be found in the district among others.  Listed on the National Register of Historic Places in 1975 with a boundary increase in 1988, the district includes 73 structures.