WebThe Thérain (French pronunciation:) is a river in France, tributary of the Oise. It is 94.4 km (58.7 mi) long. It rises between Saint-Michel-d'Halescourt and Grumesnil in Seine-Maritime at 175 meters elevation. It flows generally southeast, through Songeons, Milly-sur-Thérain, Beauvais, Hermes and Mouy, and joins the Oise at Creil.