The Sir John Johnson Manor House was originally built within the years of 1782 and 1792 by Sir John Johnson’s command as part of a mill site. Mills were required to maintain a successful and thriving village and the Raisin River allowed for such an establishment. The Manor House at the time was built as a small log cabin to serve as a temporary home possibly for Sir John Johnson, but to also serve as the home for the miller. The village that would eventually become Williamstown, named after Sir John Johnson’s late father, would be known as Johnstown, Johnson’s Mill’s or Sir John Johnson’s Mills” due to how important the mill site was to the village.
On July 22nd, 1819 the property was sold to Hugh McGillis, a retired fur trader and clerk. The property at the time included the house, the Village of Williamstown and the surrounding countryside. Hugh McGillis was able to afford such a thing due to his work with the North West Company where he started off as a clerk and eventually became a partner of the Company. During Hugh McGillis’s time in the house, the West addition of the house was added on which acted as a Summer Kitchen. Hugh McGillis is also the one who donated the land which St. Mary’s Church was built.
After Hugh McGillis came his Nephew, John McGillis. He owned the land from 1848 and 1872. During his time of ownership, he added on the two story gothic addition on the Eastern side of the building, and also built the barns for livestock. He also continued to look after the two mills and managed to increase operation during his time there, possibly due to upgrading the mill equipment.
Between the years 1872 and 1897 the land was owned by Murdoch McLennan. There were no new developments to the property during this time except for to the mills themselves. In 1879, the Saw Mill was leased to various millwrights, until eventually men by the names of Dingwall and Mcdonell leased in 1897 and eventually ceased operations of the mill completely in the same year.
1897 to 1938 was the era of ownership by Lt-Colonel D. M. Robertson and residence of Gibson P. Shaw. During this time, very little was done to the house itself but the grounds were used for a more varied assortment of crops and livestock compared to growing solely wheat. This included potatoes, oats, barley, corn and turnips. There was also a tobacco field near the barns. Animals living on site included hogs, horses and a bit of cattle. In 1914, the Saw Mill was completely non-functional and the Gristmill was being used primarily for livestock feed. The Grist mill ceased any operations in 1934.
1938 to 1956 is known as the Devaux era, when the Devaux Family lived in the house. The Devauxs used the barns mostly for pure bred race horses and pure bred cattle of the highest quality, but only up to 1954 when a fire destroyed the barns and were never rebuilt. The mills were also both taken down around this time but it is uncertain of what year exactly. During their stay the flag pole and cannons were added to the yard as décor, the flagpole and one canon still stand today. The Devauxs were the last family to live in the house.
Following the Devaux Family ownership went to Les Soeurs du Sacre Coeur (the Sisters of the Sacred Heart) from 1956 to 1971. The sisters ended up selling most of the farm land and only kept a few of the gardens for growing vegetables. During this time around 1959 or 1960 the St. Lawrence Seaway Development Commission was seeking to purchase the Sir John Johnson Manor House and move it to be part of Upper Canada Village. A local woman by the name of Llewella Dunlop worked very hard with the Sisters to ensure that Williamstown would not lose the Manor House.
From 1971 onwards, the Manor House has been under the care of Parks Canada, along with the Sir John Johnson Manor house Committee. In 1975, the East wing was converted into the Williamstown Branch of the Library, which is where it remained until 2017 when it moved to St. Mary’s Center. In the 1990s, the Committee also took ownership of land records of South Glengarry and opened the Glengarry Archives which operate out of the building to this day.
In 2013, the Committee submitted a business plan and proposal to Parks Canada to fix and restore the Manor House’s structure as well as add an Inn to the upstairs. As of 2017, work has been underway and the Manor house stabilization is complete. Currently, the Committee is working towards restoring the rest of the building and fundraising for running the Manor House Inn.