Casgrain is a French Canadian surname. Notable people with the surname include:
Charles Eusèbe Casgrain, Ontario physician and political figureCharles-Eusèbe Casgrain, lawyer and political figure in Lower CanadaHenri-Raymond Casgrain, French Canadian Roman Catholic priest, author, and publisherJoseph Philippe Baby Casgrain, Quebec surveyor, civil engineer and political figureLéon Casgrain, Canadian politicianPhilippe Baby Casgrain, Quebec lawyer, author and political figurePierre-François Casgrain, Canadian politician and Speaker of the Canadian House of CommonsThérèse Casgrain, feminist, reformer, politician and senator