The Grasse River or Grass River (per 1905 decision of the U.S. Board on Geographic Names) is a river in northern New York, in the United States. The river mainly flows northeast from the foothills of the Adirondack Mountains into the St. Lawrence Valley, making up what is known as the greater St. Lawrence River Drainage Basin along with other tributaries such as the Oswegatchie and Raquette rivers.