Ironsides Island is a rocky island in the Saint Lawrence River, and part of the Thousand Islands region near Alexandria Bay, New York. It is in both Jefferson and St. Lawrence counties. Most of the island lies in the Town of Alexandria, in Jefferson County, while its northeasternmost corner lies in the Town of Hammond, in St. Lawrence County. It was donated by Readers Digest William Browning to the Nature Conservancy in the 1960s to serve as a rookery for Great blue herons. Over a thousand herons return to breed every April. It was declared a National Natural Landmark in April 1967.