Saint-Ouën-des-Vallons is a former commune of 174 people (1999). It is found in the Pays de la Loire region in the Mayenne department in the northwest of France. On 1 January 2019, the commune was unified with Montsûrs-Saint-Céneré, Deux-Évailles and Montourtier, and the new municipality took the name of Montsûrs.