The Middlesex County Hospital was operated by Middlesex County from the 1930s until 2001. Its property straddles the towns of Waltham and Lexington, Massachusetts. Originally a tuberculosis hospital, it eventually became the county hospital for Middlesex until its closure. The property was sold and redeveloped into a condominium community. It is located near the old Metropolitan State Hospital, which was closed in 1992 and has also been redeveloped into housing.

• Middlesex County Sanitarium on the Asylum Project