Heathfield
The house which stood near this site was constructed prior to 1841, and purchased in 1865 by Prof. James Williamson of Queen's University. His wife, Margaret, was a sister of Sir John A. Macdonald, who became the first prime minister of the Dominion of Canada. Prof. Williamson leased the building to the Conservative leader, but retained a portion for his own use. Macdonald installed his unmarried sister, Louisa, in the house, and it served as his residence during his visits to Kingston 1865-1878. Later "Heathfield" was occupied by the Sisters of Providence of St. Vincent de Paul, and was demolished in 1964.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.