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
Samuel de Champlain growth of New France in the St. Lawrence River valley until his death in 1635. Champlain is memorialized as the "Father of New France" and "Father of Acadia", and many places, streets, and structures in northeastern North America bear his name, or have monuments established in his memory. The most notable of these is Lake Champlain, which straddles the border between northern New York and Vermont, extending slightly across the border into Canada. In 1609 he led an expedition up the Richelieu River and explored a long, narrow lake situated between the Green Mountains of present-day Vermont and the Adirondack