Thornhill was founded in 1794. Its first settlers on Yonge Street in Thornhill were Asa Johnson (who settled on the Vaughan side) and Nicholas Miller (who settled on the Markham side). Of particular importance was the arrival of Benjamin Thorne in 1820, who was operating a gristmill, a sawmill, and a tannery in the community. The settlement came to be known as Thorne's Mills, and later, Thorne's Hill, from which its current name is derived.
Between 1830 and 1848, Thornhill experienced a period of continued growth and prosperity. The business district of Thornhill developed on its portion of Yonge Street, between Centre Street and John Street.Stagecoaches travelled between Holland Landing (Lake Simcoe) and York (Toronto) as Yonge Street's road conditions improved with new stonework. During this prosperous period, several churches, many of which are still standing today, were constructed.
Thornhill's location along Yonge Street, a major transportation route, proved to be beneficial to the community's growth throughout much of the twentieth century. The implementation of an electric street railway along Yonge Street in 1898 towards Kleinburg, Georgina, King and Toronto meant that, for the first time, it was possible for people to reside in Thornhill and work in Toronto. By the 1920s, the prevalence of the automobile further facilitated travel along Yonge Street. [Courtesy of Wikipedia]