Its territory can be divided into three main geographical areas. The first is constituted of the estuary of the Saint Lawrence River and its islands. Second are the plains, which includes the Saint Lawrence Lowlands, which run from east to west and covers the northern portion of the Montmagny RCM, and is characterized by its arable soils. The Appalachians is the final geographic region of the area, taking up approximately 80% of the area. A series of peaks and ledges can be found here, and the Notre Dame Mountains dominate its landscape, which can reach an altitude of up to . Mixed forest covers the south of the RCM.