High Quality Content by WIKIPEDIA articles! Cat Island is a barrier island off the Gulf Coast of the United States. The island is named for raccoons which Spanish explorers mistook for cats. It is unknown who discovered Cat Island. It was called Isle-aux-Chats and Isola de Gati in French and Italian, respectively. It is within the jurisdiction of Harrison County, Mississippi. The western half and southern tip of the island is part of the Gulf Islands National Seashore.