Thornhill has a very ethnically diverse population. It is particularly known for its large Jewish community: approximately 40% of the population are Jewish, including many Israeli and Russian immigrants. This community comprises the majority of Thornhill-Vaughan and nearly a quarter of Thornhill-Markham. It is home to one of the largest Orthodox Synagogues in North America.

Located on Toronto's northern border, Thornhill is divided in half between the Town of Markham and the City of Vaughan, and runs along both the east and the west sides of Yonge Street. Today Thornhill has become a bedroom community for those working in the Greater Toronto Area

Thornhill's growth since the 1960s and 1970s has been largely connected to its location bordering what is now the City of Toronto, Thornhill is considered one of the Greater Toronto Area's more upscale communities.