Prudence Island is the third largest island in Narragansett Bay in the U.S. state of Rhode Island and part of the town of Portsmouth. It is located near the geographical center of the bay. It is defined by the United States Census Bureau as Block Group 3, Census Tract 401.03 of Newport County, Rhode Island. As of the 2000 census the population was 88 people living on a land area of 14.43 km² (5.57 sq mi).