Mongaup Valley is a hamlet (and census-designated place) in Sullivan County, New York, United States. The community is located along New York State Route 17B 5 miles (8.0 km) west of Monticello, and along the Mongaup River. Mongaup Valley has a post office with ZIP code 12762, which opened on June 22, 1848.

Notable person

• Stephanie Blythe (born 1970), mezzo-soprano