Montreuil-sur-Ille (, literally Montreuil on the Ille; ; Gallo: Móstroelh) is a commune in the Ille-et-Vilaine department of Brittany in northwestern France. The commune's name reflects its location on the Ille river.
Inhabitants of Montreuil-sur-Ille are called in French Montreuillais.