McIlwain is a surname. Notable people with the surname include:
Charles Howard McIlwain (1871–1968), American historian and political scientist
Dallas McIlwain (born 1982), Australian rugby league player
David McIlwain (1921–1981), English science fiction writer
John McIlwain, American urban planner
Stover McIlwain (1939–1966), American baseball player
Wally McIlwain (1903–1963), American football player
Zach McIlwain (born 1986), American national veterans advocate