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
Tupper Lake (town), New York water body in the southwest part of the town, and crosses the county line into St. Lawrence County. New York State Route 3 joins New York State Route 30 at Tupper Lake village; the highways are conjoined through the eastern part of the town. The Raquette River, a northwest flowing tributary of the St. Lawrence River, flows past Tupper Lake village. As of the census of 2000, there were 6,137 people, 2,429 households, and 1,530 families residing in the town. The population density was 52.2 people per square mile (20.1/km²). There were 3,118 housing units at an average density of