The origins of the Village of Thornhill date back to 1792 when Governor Simcoe explored the area for a suitable road and town site north of York (Toronto).
By 1794, a trickle of permanent settlers arrived at the site of Thornhill and began to claim their Crown Grants of 200 acres stretching a quarter of a mile along Yonge Street and backing east and west to the first Concessions at present-day Bayview and Bathurst Streets.

The First Official Settlers on Yonge Street in Thornhill were Asa Johnson and Nicholas Miller, both claiming their Grants in 1794, Miller on Lot 34 Markham, near present day Bayhill Mews and Johnson at Lot 29 Vaughan, (in the area of the Arnold House).

Through the efforts of these first settlers, a prosperous village arose on the banks of the Middle Don. In 1829, this village supported four sawmills, two distilleries, three blacksmith shops, three harness makers, a grist mill, tannery and a carding and fulling mill. Shortly thereafter, the first post office was installed.

Many events detail the evolution of this village to its present state: The Rebellion of 1837; the early prominence and unhappy passing at his own hand, of Benjamin Thorne in 1848; the serious flooding along the Don; the epidemics that swept through the village; Prohibition and the closing of local taverns; the arrival, over time, of five of the Group of Seven to reside here; and finally, in the post-war years, the pressures and changes of rapid land development.

The formation of the historic society in 1974 was in response to the homogenizing influences and worst excesses of this wholesale land development. At present over one hundred historic buildings stand as reminders of the past. The Society has also commemorated fifteen sites with historic plaques. The Thornhill Village (Wheatsheaf) Festival was started in 1977 in part to draw attention to the "Old Town". Both sides of Thornhill are designated as Heritage Conservation Districts.