Fort Matanzas National Monument is a United States National Monument run by the National Park Service. The Monument consists of a 1740 Spanish fort, Fort Matanzas, and about 100 acres (0.4 km²) of salt marsh and barrier islands along the Matanzas River on the northern Atlantic coast of Florida. It is operated by the Park Service in conjunction with the Castillo De San Marcos National Monument and several sites in the city of St. Augustine.
The United States never used the fort and it became a ruin. In 1916, restoration work began on the badly deteriorated fort. In 1924, National Monument status was proclaimed. It was transferred from the War Department to the National Park Service on August 10, 1933. As an historic area under the Park Service, the National Monument was listed on the National Register of Historic Places on October 15, 1966.
The Fort is accessible only by guided boat tours. Hiking trails are available on the barrier island.