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
Lake Champlain Vermont are on the lake's western and eastern shores, respectively, and the village of Ticonderoga, New York is in the region's southern part. The Quebec portion is in the regional county municipalities of Le Haut-Richelieu and Brome-Missisquoi. There are a number of islands in the lake; the largest include Grand Isle, Isle La Motte, and North Hero, all part of Grand Isle County, Vermont. The Champlain Valley is the northernmost unit of a landform system known as the Great Appalachian Valley, which stretches between Quebec, Canada, to the north, and Alabama, US, to the south. The Champlain Valley is a