I visited this small museum after going to the JFK Library which is across the street. A nice collection of exhibits telling about the founding of the Commonwealth, it's more geared towards a younger audience.
The highlight of the museum is the room where they have the bronze plate that Paul Revere made of the Boston Massacre, Charter of Massachusetts, Charter of the Bay Colony, Copy of the Declaration of Independence made on the 50th anniversary, Bill of Rights and the Massachusetts Constitution.
It is worth a visit if in the area, admission is free.