It encompasses a portion of Ontario previously included in the electoral districts of Markham—Unionville and Thornhill.

[3] Markham—Thornhill was created by 2012 federal electoral boundaries redistribution and was legally defined in the 2013 representation order.

It came into effect upon the dropping of the writs for the 2015 federal election.

[4] Markham—Thornhill loses more people than any other federal electoral district in the 905 region.

Ethnic groups: 42.8% Chinese, 27.5% South Asian, 12.7% White, 3.8% Black, 2.7% Filipino, 3.0% West Asian, 1.3% Korean Languages: 29.5% English, 18.7% Cantonese, 13.8% Mandarin, 7.6% Tamil, 3.1% Urdu, 2.3% Punjabi, 2.0% Persian, 1.9% Gujarati, 1.3% Tagalog, 1.0% Korean Religions: 28.2% Christian (13.5% Catholic, 2.4% Christian Orthodox, 1.0% Anglican, 11.3% other), 14.3% Hindu, 10.8% Muslim, 4.7% Buddhist, 3.1% Jewish, 2.2% Sikh, 36.1% none Median income: $32,400 (2020) Average income: $47,640 (2020) This riding has elected the following members of Parliament: A by-election was held on April 3, 2017, following John McCallum's appointment as Ambassador to China on January 10, 2017.