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
Fort Montgomery (Lake Champlain) Fort Montgomery (Lake Champlain) Fort Montgomery on Lake Champlain is the second of two American forts built at the northernmost point of the American part of the lake: a first, unnamed fort built on the same site in 1816 and Fort Montgomery built in 1844. The current massive stone fortification, the second fort, was built between 1844 and 1871 at the Canada–US border of Lake Champlain at Island Point in the village of Rouses Point, New York. Construction was begun on the first fort at this location, an octagonal structure with walls, in 1816 to protect against an attack from