Lewis County is a county located in the U.S. state of New York. As of the 2010 census, the population was 27,087. It is named after Morgan Lewis, the Governor of New York when the county was established. Its county seat is Lowville.
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.