The municipality has the largest surface area in Lotbinière Regional County Municipality, with a surface area of around 177.43 km2 and a population density of around 16.4 inhabitants/km2.
Saint-Gilles is named after the seigneurie of Saint-Gilles of which it was part. It was granted in 1738 to Gilles Rageot de Beaurivage (1689-1754), an important merchant from Quebec.[4]