Pierrefonds is a former city in southwestern Quebec, Canada. It is located along the Rivière des Prairies on the northwestern part of the Island of Montreal. It was merged into Montreal on January 1, 2002, and is today part of the borough of Pierrefonds-Roxboro.
Its origin dates back to the eighteenth century, and is intimately linked to that of Sainte-Geneviève, which was composed at the time of Pierrefonds, L'Île-Bizard, Sainte-Geneviève, Roxboro and Dollard-des-Ormeaux.
In 1904, following several previous divisions, the Town of Sainte-Geneviève was split into two new villages: Sainte-Geneviève and Sainte-Geneviève de Pierrefonds. This was the first appearance of the name Pierrefonds. At the heart of the conflict leading to the separation was the notary and local member of the Legislative Assembly Joseph-Adolphe Chauret, who, in 1902, had a "seigniorial" residence built for himself reminiscent of the community of Pierrefonds in France’s Department of Oise. He named his thatched home "Château Pierrefonds", apparently providing the name for the future city.
In 1935 the two villages of Sainte-Geneviève and Sainte-Geneviève de Pierrefonds merged once again into a single village called Sainte-Geneviève. The name Pierrefonds disappeared, resurfacing on December 18, 1958, when the rest of the territory of the old parish became the City of Pierrefonds.