When counties were established in New York State in 1683, the present Lewis County was part of Albany County. Lewis County is located in northwestern New York State, slightly east of due north from Syracuse. The eastern part of the county is in the Adirondack Park. A good portion of the Tug Hill Plateau is in the western part of the county. The county is home to the Black River Valley. According to the U.S. Census Bureau, the county has a total area of 1,290 square miles (3,341.1 km2), of which 1,275 square miles (3,302.2 km2) is land and 14 square miles (36.3 km2) (1.12%) is water.