It is located at 6 Washington Street in the city center, in an architecturally distinguished Classical Revival building constructed in 1907–08 with funds bequested by Leonard Frost Aldrich, a local businessman, and was substantially enlarged in 2000.

It is a two-story building, with a steel frame and brick veneer exterior trimmed in local granite.

The outer bays have three-part windows on each level, set in a shared keystoned granite surround.

The stairway leading to the entrance is framed by granite sidewalls topped by original Beaux-Arts iron globe light fixtures.

The city council originally sought to have a building completely faced in local granite (the city's primary business), but this was found to be cost prohibitive, and a compromise construction of brick trimmed in local granite was developed by the architect, Penn Varney of Lynn, Massachusetts.