The lands south of Burrard Inlet, where the Slocan site is located, were used by the Musqueam, Squamish Nation, and Tsleil-Waututh Nation. The site was likely used for hunting and for gathering food, medicine, and resources.

It is unknown when the site was taken by settlers. We do know that it was sold to the City of Vancouver in 1911 by an individual landowner, who had cleared the land of trees a few years prior. 

In 1911, the City of Vancouver purchased the site to build an isolation hospital. The hospital opened in November 1912 and was used to care for people with smallpox. It was made up of three main buildings: an administrative building and two wings on either side, one for men and one for women. The hospital was in operation until the late 1920s when smallpox was brought under control with vaccination.

The buildings were next used to treat school-aged children who had been exposed to TB. After some renovations, the doors of the Vancouver Preventorium opened in November of 1931. The facility included 25 beds, a school, a playroom, a library, and landscaped grounds.