The Boston Police Department (BPD), dating back to 1838, holds the primary responsibility for law enforcement and investigation within the city of Boston, Massachusetts. It is the third oldest municipal police department in the United States, after those of Philadelphia, Pennsylvania and Richmond, Virginia. The BPD is also the 20th largest law enforcement agency in the country and the 3rd largest in New England behind the Massachusetts State Police (2100 officers) and the Massachusetts Department of Corrections (4,000 officers).