In 1880, J.P. Withers, a Canadian Pacific Railway officer, set up home in Rosemère. Impressed by the compelling charm of the many wild-growing roses, he decided to call the place "Rose,” to which he simply added the suffix "mere,” an old Anglo-Saxon word for swamp. He then went to Ottawa to register the name in use ever since.

In the early 20th century, the region—now known under the name Rosemère—owed its growth to the presence of the Canadian Pacific Railway. In 1901, Rosemère opened the doors of its first post office, and in 1936, the area's newly built chapel was inaugurated.

What follows are well-known chapters in Rosemère's local history for many of the residents, especially the elder residents: the regatta on the Mille-Îles River (formerly called Jesus River), and the "Garths” against the "Tylees” competition. Later, the Skeltons, the Earls and the Blachfords took up summer residence, and the Gilmours managed Thorncliffe House, a fine and well-known restaurant which burnt down in 1982. Rosemère's Country Club was founded in 1920; and the Golf Club two years later, in 1922.