The Château du duc d'Épernon is a château, built on the site of a medieval castle located in Fontenay-Trésigny, in the Brie region of France, 43 km (27 mi) southeast of Paris. It stands alongside the Bréon stream and next to the Church of Saint-Martin, in the heart of a once walled old town, the history of which is closely linked to the history of the château. The castellans were lords of Fontenay-en-Brie during the Old Regime.