Lac-Mégantic is located at the eastern part of the Estrie administrative region, in the Regional County Municipality of Le Granit, approximately from the United States border. The Chaudière River has its source in Lake Megantic and empties into the St. Lawrence River, some further north, near Lévis (within the former city of Saint-Romuald). The Town of Lac-Mégantic is located from Mont Mégantic.