The neighbourhood is actually names after the “Summer Hill” residence, a fabulous regency cottage that was built in 1842 by a transportation baron named Charles Thompson. Summer Hill is not around today, but was was situated on the crest of the hill where the houses on Sumerhill Gardens are.
The former 200-acre estate stretched from Yonge St. to Mt. Pleasant Road. On the site, Thompson created the “Summer Hill Spring Park and Pleasure Grounds’, which was an amusement park that featured rides, games, swimming and a dance pavilion located inside the house.
In the 1860s, Thompson’s heirs subdivided the estate, and from the that point onward the development of the new found community revolved around the railway. The first residents here worked at North Toronto Railway Station in the 1880s (which is the current Summerhill LCBO). The station was rebuilt in 1916.
In the 1920s the Canadian Pacific Railway made Summerhill their main Toronto station. When the railway station closed this area went into a period of decline that lasted until the Summerhill subway station opened in 1954 (prior to this was probably a good time to buy real estate here!).
Interestingly enough, the former Summer Hill Coach House, circa 1865, is still standing today at the rear of 36 Summerhill Gardens. This house, with its distinctive slate roof is visible from the south part of the Rosehill Reservoir.
Sources: torontoneighbourhoods.net, carollome.com