Padre Island sand dunes. Padre Island is the largest of the Texas barrier islands and is the world's longest barrier island. It is part of the U.S. state of Texas. The island is located along Texas' southern coast of the Gulf of Mexico and is noted for its white sandy beaches at the south end.he town of South Padre Island is located on its southern end, but the island as a whole is sparsely populated. The central part of the island is preserved in a natural wild state as Padre Island National Seashore. Since 1964, the island has been divided by the artificial Port Mansfield Channel.