It covers the Thornhill neighbourhood, which is split between Vaughan and Markham, and was created in 1996 from parts of Markham—Whitchurch—Stouffville and York North ridings.

It consists of the part of the city of Vaughan that is east of Highway 400 and south of Rutherford Road, and the part of the city of Markham west of Bayview Avenue.

It is one of only two ridings in Canada with a Jewish plurality (the other being Mount Royal in Quebec). 32.8% of the population is Jewish, the highest in Canada. Thornhill also has the highest percentage of Russians (12.9%) of all Canadian ridings (implying the presence of a strong community of Russian Jews).

The Thornhill riding has the highest percentage of population with an educational attainment of "University certificate or diploma above bachelor level" (i.e. above-bachelor-level certificate or diploma other than doctorate, master, or medicine etc. degrees) with 5.0%.

The riding lost all of its territory east of Bayview Avenue to Markham-Thornhill, and gained a small fraction from York Centre in the 2012 redistribution.

Ethnic groups: 68.2% White, 7.6% Chinese, 6.5% South Asian, 4.6% Filipino, 3.7% Korean, 3.3% West Asian, 1.9% Black, 1.1% Southeast Asian
Languages: 49.9% English, 13.0% Russian, 6.2% Chinese, 3.1% Persian, 3.2% Korean, 3.7% Hebrew, 3.0% Italian, 2.2% Tagalog, 1.7% Spanish 1.4% French, 1.0% Gujarati
Religions: 37.5% Christian (18.8% Catholic, 6.2% Christian Orthodox, 2.0% Presbyterian, 1.6% Anglican, 1.5% United Church, 7.3% Other Christian), 37.1% Jewish, 4.3% Muslim, 3.4% Hindu, 2.0% Buddhist, 14.7% None.
Median income: $30,798 (2010)
Average income: $47,097 (2010)

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