The Loir is a river in western France. It is a left tributary of the Sarthe River. Its source is in the Eure-et-Loir département, north of Illiers-Combray. It joins the river Sarthe in Briollay, north of the city Angers.It is indirectly a tributary of the Loire, and runs roughly parallel to it and slightly north of it for much of its length, and so might be regarded as a Yazoo type river.