Vly Mountain is a mountain located in the town of Halcott, New York, United States in Greene County. The mountain is part of the Catskill Mountains. Vly Mountain is flanked to the northwest by Bearpen Mountain.
The north side of Vly Mountain drains into Little West Kill, thence into Schoharie Creek, the Mohawk River, the Hudson River, and into New York Bay. The east side of Vly Mtn. drains into West Kill, thence into Schoharie Creek. The south and west sides of Vly drain into Vly Creek, thence into Bush Kill, Dry Brook, the East Branch of the Delaware River, and into Delaware Bay.