The original 380 acre site for the Mental Health Centre Penetanguishene (MHCP) was chosen by Governor John Graves Simcoe as a naval and military base to protect the Upper Great Lakes from American threats in the aftermath of the War of 1812. During the 1960's about 60 acres were turned into a historical park to preserve the early history of the site.

The military site was widely visited by prestigious people until it was decommissioned and turned over to the Government of Upper Canada in 1855. 

The Boys Reformatory of Upper Canada was established in the abandoned barracks in 1859, continuing the economic link between the local people and government institutions. The barracks were consumed by fire in 1870, so the location of the reformatory was moved up the hill and a new building was constructed with the boys providing the labour. Stones from the old barracks were used as a foundation and new stone was taken from Quarry Island in Severn Sound. The resulting structure, currently known as the MHCP Administration Building, is the oldest on the grounds and one of several registered historic sites. How did the grounds eventually become a major psychiatric hospital?         

By 1904 it was clear that, for a number of reasons, the Boys Reformatory was not suitably located in Penetanguishene. The remaining boys were scattered to other provincial institutions or community placements and the building was converted into an "asylum for the insane."  Most staff members lived on the grounds either in residential sections of the larger buildings or in white clapboard houses, some of which have been preserved as historic sites or active treatment areas. The Superintendent lived in the large Victorian mansion on the edge of the grounds which is now the Georgianwood Addiction Centre.  Since 1974, MHCP has had a separate Administrator and Medical Director (now called Psychiatrist-in-Chief). All staff now reside off the grounds.

In 1933, the first four wards of the Oak Ridge Division were constructed. Originally intended to provide custodial care to the "criminally insane," Oak Ridge was the only institution of its kind in Canada at the time. During this period the name of the entire institution was changed to Ontario Hospital. Prior to 1933, mentally disordered offenders were shunted around the province to locations of convenience. The Oak Ridge Division eventually grew into an active treatment centre. Since patients rarely moved on in the early days, four additional wards were added to Oak Ridge in the mid-1950's bringing the patient capacity to 300.

In 1967, the Brebeuf and Bayfield buildings opened. Originally designed as apartment-style living quarters to simulate life in the community, both buildings are now active treatment centres. Psychotropic drugs, developed in the late 1950's, and the development of a psychosocial rehabilitation model made it possible to stabilize and discharge many patients who had formerly been confined to psychiatric hospitals. The trend to de-institutionalize patients to appropriate community placements continues to this day. Upper Brebeuf is now location of the Psychosocial Rehabilitation Program, which deals with patients requiring long-term care. The lower floor houses the Forensic Services Program. Lower Bayfield is now the location of the Geriatric Services Program.

Around 1970, the number of patients in residence at both divisions reached a historical high of about 650. In 1971 the name of the institution was changed to the Mental Health Centre and work was begun on the newest major structure on the site - the Toanche Building. The six levels of the Toanche Building provide various programs, including the Admission Assessment Program and the Bayview Dual Diagnosis Program.

Over the years many buildings have been demolished, others have been built and some, such as the Administration Building, have been extensively renovated and put to other uses. Both divisions currently have a combined maximum of 300 beds, but MHCP now also acts as a resource and operates an Outpatient Services Department located in Midland. The latest construction on the grounds is the Oak Ridge Activity Centre which provides a pool and gym patient use.