In the 1920s,30s and 40s, where we now see a high-rise residential and commercial area, there was a racetrack complete with a grandstand with bleachers that could seat 4,000 people, a clubhouse, and stables for up to 610 horses. Mathilda Bryan and James O’Hara, a couple from Baltimore bought the land and built the racetrack. It opened on 31 May 1920 and operated for 32 years; the last race ran on 23 June 1952. When it opened, Toronto had three other racetracks: Woodbine, Dufferin, and Long Branch. The thoroughbreds which ran at Thorncliffe were among Canada’s finest. It was considered Toronto’s most attractive track, and was quite popular, but it was difficult to reach. Although the possibility of a viaduct had been talked about since 1911, the popularity of horse racing and of Thorncliffe provided the final stimulus to get The LeasideViaduct built.
Information from “A Glimpse of Toronto’s History” MPLS # 213