The Summerhill neighbourhood is named after 'Summer Hill' house, a magnificent Regency cottage built in 1842, by transportation baron Charles Thompson. Summer Hill house stood on the crest of the hill where the houses on Summerhill Gardens are located today.

Thompson's two hundred acre Summer Hill estate stretched from the present day Yonge Street to Mt. Pleasant Road. On this site, Thompson established the 'Summer Hill Spring Park and Pleasure Grounds', an amusement park that featured rides, games, swimming and a popular dance pavilion that was located inside the Summer Hill house. Thompson's heirs subdivided the sprawling Summer Hill estate in the 1860's.

From the 1880's onward, Summerhill's development revolved around the railway. The first residents of this neighbourhood worked at the North Toronto Railway station, which was established on Yonge Street near Summerhill in the 1880's. This station - rebuilt in 1916 - is distinguished by its grand clock tower and now serves as the neighbourhood LCBO.

In the 1920's, the Canadian Pacific Railway made Summerhill their main Toronto station. When Summerhill station closed, this neighbourhood went into a period of decline that lasted until the Summerhill subway station opened in 1965. Summerhill has enjoyed a position of prominence among Toronto neighbourhoods ever since.