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
Ogdensburg, New York the City of Ogdensburg in 1868. It is located between Brockville, Ontario to the west and Massena, New York to the east. Beginning in the mid-19th century, Ogdensburg expanded on its role as a port city on the St. Lawrence River, becoming an important trading city and station as railroads were developed in northern New York and southeastern Canada. The Ogdensburg & Lake Champlain Railroad (later Rutland Railroad) (1849), Rome, Watertown & Ogdensburg Railroad (1853) and Portland & Ogdensburg Railway (never completed), all constructed lines through the area connecting the historic towns. In 1940 the town was the site of