Casgrain is a French Canadian surname. Notable people with the surname include:
- Charles Eusèbe Casgrain, Ontario physician and political figure
- Charles-Eusèbe Casgrain, lawyer and political figure in Lower Canada
- Henri-Raymond Casgrain, French Canadian Roman Catholic priest, author, and publisher
- Joseph Philippe Baby Casgrain, Quebec surveyor, civil engineer and political figure
- Léon Casgrain, Canadian politician
- Philippe Baby Casgrain, Quebec lawyer, author and political figure
- Pierre-François Casgrain, Canadian politician and Speaker of the Canadian House of Commons
- Thérèse Casgrain, feminist, reformer, politician and senator