Thornhill is located on the northern border of the city of Toronto. The former municipal village of Thornhill is now a community and postal designation divided along Yonge Street between the municipalities of Vaughan to the west and Markham to the east, with a population of 106,000. 

Originally centred on Yonge between Centre Street and John Street, the boundaries of the community are now generally considered to be Dufferin Street to the west, Highway 7 to the north, Steeles Avenue to the south, and Highway 404 to the east.  Like most of the urbanized for Greater Toronto Area villages outside of the City of Toronto, such as Woodbridge, Maple and Unionville, Thornhill has retained postal designation for addresses within the former village’s boundaries, and local newspapers, sports teams, and schools continue to operate under the Thornhill name.

The village was founded in 1794, and the settlement came to be known as Thorne’s Mills, and later Thorne’s Hill, after Benjamin Thorne, who arrived in the community in 1820 and operated a gristmill, sawmill, and a tannery.  The business district developed along Yonge Street in the 1830s and 1840s, benefiting from traffic along the major route.  During this period, several churches were built that are still standing today.

Thornhill has grown significantly since the 1960s and 1970s due to its proximity to Toronto, with large housing developments appearing in the 1980s, such as the Spring Farm area near Bathurst and Clark, and growth has continued steadily since then.  

More recently, the Thornhill Town Centre has been developed at the corner of Bathurst and Centre as an upscale shopping development, just north of the Promenade Shopping Centre, and the area is continuing to attract condominium and retail development.  Development on the Vaughan side is pushing north, into the area of the former village of Maple.  The North Thornhill Community Centre opened in 2010 to serve this growing population.

Thornhill is home to an ethnically diverse population and significant numbers of visible minorities, with Chinese residents accounting almost 11% of total residents. Thornhill is notable for its large Jewish community, and is home to numerous synagogues and schools, particularly Ashkenazi and Sephardic Orthodox synagogues.