Sediments of the Woodbine Group exposed in northeastern Texas were deposited along the southwestern margin of Appalachia as a series of near-shore, shoreline, distal lowland swamp, lake, and fluvial deposits during a regression of the Western Interior Seaway in early and middle Cenomanian time. The Lewisville Formation (upper Woodbine Group) of north Texas preserves the most diverse terrestrial fossil assemblage known from Appalachia, but remains of small ornithischian dinosaurs have been conspicuously absent from it. An almost complete left dentary from the Lewisville Formation represents a new, small-bodied ornithopod taxon, Ampelognathus coheni gen. et sp. nov. The dentary is generally similar to those in non-iguanodontian ornithopods such as Hypsilophodon, Changchunsaurus, Haya, and Convolosaurus. Ampelognathus occupied an expected but previously missing component of the ‘mid’ Cretaceous terrestrial fauna of southwestern Appalachia. The growing diversity of fossil vertebrates and renewed paleobotanical study in the Lewisville Formation reinforces the importance of the unit’s fossil record for understanding eastern North American terrestrial ecosystems during an important transitional period in the earliest Late Cretaceous.