Rondout Creek is a 63.3-mile-long (101.9 km) tributary of the Hudson River in Ulster and Sullivan counties, New York, United States. It rises on Rocky Mountain in the eastern Catskills, flows south into Rondout Reservoir, part of New York City's water supply network, then into the valley between the Catskills and the Shawangunk Ridge, where it goes over High Falls and finally out to the Hudson at Kingston, receiving along the way the Wallkill River.