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
New York State Route 373 from the town of Chesterfield to the state of New York as part of a highway maintenance swap between the state and Essex County. New York State Route 373 New York State Route 373 (NY 373) is a short state highway in Essex County, New York, within Adirondack State Park. It begins at U.S. Route 9 (US 9) and proceeds eastward, ending at a ferry landing on Lake Champlain. It intersects two county routes, several local roads, and a reference route—NY 912T—which connects it with US 9. NY 373 is the only connector between US 9 and the hamlet of