The part in the City of Markham is restricted its portion of Thornhill itself (but does not include it all) west of Bayview Avenue.

[4] The district of Concord and Vaughan Metropolitan Centre occupies the northern and western parts of the riding.

[7] The riding has a higher rate of postsecondary certificates, diplomas, and degrees than the Ontario average (66% compared to 55% for those aged 15+).

[8] Religion in Thornhill (2021)[10] Ethnic groups: 57% White, 11.3% Chinese, 7% West Asian, 6.3% South Asian, 5.1% Korean, 4.8% Filipino, 2.6% Black, 1.5% Latin American, 1.1% Southeast Asian The riding was first established in the 1996 redistribution from parts of York North and Markham—Whitchurch—Stouffville, consisting of the part of Vaughan east of Highway 400 and south of Rutherford Road, and the part of Markham west of Highway 404.

[17] Similarly to the previous election,[12] the Liberals had nearly swept the province of Ontario, this time winning all but two seats.

[7][22][23] In the 2004 election, many ridings with large Jewish populations, Thornhill among them, started shifting toward the Conservative Party.

[26] In March 2008, she was appointed National Revenue critic by Opposition Leader Stéphane Dion.

[27] In the 2008 election, the Conservative Party chose Peter Kent, an established media personality who had run in Toronto-St. Paul's in 2006,[25] as their candidate.

Kent would end up winning the riding with 49% of the vote compared to Kadis' 39%, possibly due to the fact that Conservative Prime Minister Stephen Harper promised continued support for Israel.

It also signalled Prime Minister Harper's determination to increase support in the Greater Toronto Area.

[5] Markham was initially added to the name before Kent suggested reverting it back to "Thornhill".

[38] In 2019, Kent won his fourth consecutive election with 54.6% of the vote to Liberal candidate Gary Gladstone's 35.4%.