Mērsrags is a small harbour town in Talsi Municipality, in the Courland region of Latvia. It lies on the west coast of the Gulf of Riga, beside Lake Engure, and is surrounded by extensive woodlands.
The former Mērsrags municipality had a total area of 109 km², of which 63.7% was woodland and 20.4% was covered by Lake Engure. Its coastline ran for about 12 km. The town centre is roughly 42 km from Talsi, the main city of the area, and about 95 km from Riga, the capital.