Washington County, New York is part of the Great Appalachian Valley (also known simply as the 'Great Valley') which is a long narrow valley strip often between tall mountain ranges. The county transitions from the Taconic Mountains to the Adirondack Mountains, and from the Lake Champlain Valley to Hudson River Valley. Much of the county is part of the slate valley of the Upper Taconic Mountains (Taghkanic, meaning 'in the trees'). The eastern boundary of Washington County is the New York–Vermont border, part of which is Lake Champlain. This is also the border with New England proper. The northern end of the county is
Champlain, New York connecting New York City to the south with Montreal to the north, via Quebec Autoroute 15. Champlain is approximately south of Montreal. According to the 2010 2010 United States census, the town has a total area of , of which is land and , or 12.90%, is water. Lake Champlain and the Richelieu River are on the east edge of the town, which shares a border with Grand Isle County, Vermont. The town line to the north is the international border with Saint-Bernard-de-Lacolle, Quebec, Canada. The Adirondack Northway (Interstate 87) is a major north-south highway that begins at the Canada–United