The following is from 1856.org and used with permission. It deals specifically with Massachusetts, but I'm sure many other states have similar resources to look into.

Visit the Massachusetts State Archives and spend several hours in the files. I have done this myself and always came across unexpected, rare, and rewarding information. The staff can't do this for you, so if you contact them by phone they can only tell you to come in person and do the search yourself. The documents at the state archive cover the entire spectrum, from patient records to building plans. However, the records are chronically incomplete, vary from institution to institution, and many of the people-records are OLDER than 75 years. Here is the information for the archives:

Massachusetts State Archives
220 Morrissey Blvd., Boston, MA 02125
Telephone: (617) 727-2816

Another source of information might be the central office of the Department of Mental Health of Massachusetts, located in Boston. Best way to reach them is in writing and with a follow-up phone call. Many people searching for the records of their relatives have told me that it is difficult to get results. Oftentimes the information is kept confidential, especially in the case of former patients, and can only be requested through a court order. But you should definitely try anyway. Here is the information for the DMH:

Massachusetts Department of Mental Health
25 Staniford Street Boston, MA 02114
Telephone: (800) 221-0053 (Information & Referral Specialist)

More about the DMH:

In Massachusetts, responsibility for providing public mental health services falls under the umbrella of the Executive Office of Health and Human Services (EOHHS). DMH is one of 15 EOHHS agencies. Others include the Department of Public Health, Department of Mental Retardation, Department of Social Services, Department of Youth Services (juvenile justice), Massachusetts Rehabilitation Commission (vocational services), and Division of Medical Assistance (Medicaid).

DMH is organized into six geographic Areas, each of which is managed by an Area Director. Each Area is divided into Local Service Sites. Each Site provides case management and oversees an integrated system of state and vendor-operated adult and child/adolescent mental health services. Most planning, budget development, program monitoring, contracting, quality improvement and citizen monitoring emanate from Site and Area offices. Citizen advisory boards at every level of the organization participate in agency planning and oversight. DMH allocates funds from its state appropriation and federal block grant to the Areas for both state-operated and contracted services. This includes four state hospitals, five community mental health centers with inpatient units, adult inpatient units at two public health hospitals, contracted adult, adolescent and latency age inpatient units and latency and adolescent intensive residential treatment programs, and community- based services.

The central office of DMH, located in Boston, has three divisions in addition to the Commissioner's office - Program Operations, Clinical and Professional Services and Management and Budget. It coordinates planning, sets and monitors attainment of broad policy and standards, and performs certain generally applicable fiscal, personnel and legal functions. Some specialized programs, such as forensic.

Good Luck.