Montmagny is northwest of the Notre Dame Mountains, more commonly but unofficially called the Canadian extension of the Green Mountains as they are called in New England.

While Mont Notre Dame is the official name, the vast majority of people living in the area stretching from Quebec City to the Gaspé Peninsula refer to them as simply "the Appalachians" (French: les Appalaches), the origin of the official designation of the region comprising Quebec City's South Shore suburbia to the US border to the east and the northeast, which is known as Chaudière-Appalaches, after the mountains and the main river flowing down from them into the St. Lawrence River The city of Montmagny itself is divided by the South River (French: Rivière du Sud), where a smaller river, Bras-Saint-Nicolas, merges into it.

The confluence of waters swells into a set of falls, leading to discharge into the Saint-Lawrence a short distance west of the city.

[4] Researchers have studied the intertidal marshes of the St. Lawrence estuary at Montmagny.

A post-secondary institution, The Centre d'études collégiales de Montmagny, a hospital, named Hôtel-Dieu de Montmagny, and a provincial jail are part of the economy.