The village is mentioned twice in the Domesday Book as Moretun. At the time of the Norman invasion, the lands were part of the manor of Kirkby Fleetham held by Gospatric, son of Arnketil, with some lands held by Grim. Afterwards the descent of the manor followed that of nearby Ainderby Steeple.
The toponymy of the village is derived from the Old English word mōr for Moor and the word tun for farm, with the addition of the geographical reference to the nearby river, giving Moor farm on the River Swale.