Thornhill is a surname. Notable people with the surname include:
Alan Thornhill (born 1921), British sculptorArthur Thornhill (1850–1930), English politicianBatt Thornhill, Irish sportspersonClaude Thornhill (1909–1965), American pianist, arranger and bandleaderClaude E. Thornhill (1893–1956), American college football player and coachDorothy Thornhill (born 26 May 1955), British politician, Mayor of WatfordFrederick Thornhill (1846–1876), English cricketerGeorge Thornhill (MP) (1783–1852), English member of parliamentGeorge Thornhill (cricketer) (1811–1875), English cricketerJames Thornhill (1675/6–1734), English painterLeeroy Thornhill (born 1969), British electronic music artistLeonard W. Thornhill (1915–1942), American World War II Naval officer and pilotLisa Thornhill (born 1962), American actressMatt Thornhill (born 1988), English footballerMichael Thornhill (born 1941), Australian film producer, screenwriter, and directorPauline Thornhill, host and producer of Canadian Broadcasting Corporation's longest running regional television program, Land and SeaRoland Thornhill (born 1935), Canadian politicianSiri Thornhill, Norwegian sopranoThomas Thornhill (1837–1900), British politicianTom Thornhill (born 1952), American lawyer and politicianWilliam Thornhill (c.1500–1557), English politicianWilliam Pole Thornhill (1807–1876), English politician and landownerFictitiousRoger O. Thornhill, character played by Cary Grant in North by NorthwestErnest Thornhill, alias of The Machine in Person of Interest (TV series)