Rocky Hill is a Borough in Somerset County, New Jersey, United States, named for the Rocky Hill Ridge. It was earlier known as the Devil's Featherbed because it was difficult to travel the rocky terrain by horse and wagon. As of the United States 2000 Census, the borough population was 662. Rocky Hill was incorporated as a borough by an Act of the New Jersey Legislature on December 18, 1889, from portions of Montgomery Township, based on the results of a referendum held four days earlier.