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 America. The park was further protected in 1894 when a clause was added to the New York State constitution which banned the selling of timber from state parks. On April 16, 1827, a team of three surveyors were commissioned to determine a routing for a new highway leading from Hopkinton, a town in northeastern St. Lawrence County, to Lake Champlain. The task took 26 days, after which it was determined that the highway would meet Lake Champlain at Fort Kent. An act authorizing the construction of the highway was passed by the New York State Legislature on April 18, 1829.