The money received from Congress in 1916 was enough to do little more than stabilize the fort. In 1924, a local man, Eugene Johnson of Summer Haven, was contracted to procure, deliver, and spread oyster shells around the base ofFortMatanzasto further stabilize it. At 12 cents per barrel, by October he had delivered 3825 barrels of shell.
On October 15, 1924, using the power granted in the Antiquities Act, President Calvin Coolidge namedFortMarion(The Castillo deSan Marcos) andFortMatanzasas national monuments. During the late 1920s, extensive repair was done onFortMatanzas. The garita (sentry box), which had fallen off, was rebuilt. Iron rods were placed within the tower, and the gun deck parapet and lower walls were rebuilt. The land onRattlesnakeIslandsurrounding the fort was set aside as a bird sanctuary.
With the War Department divesting itself of obsolete forts, the forts were transferred from the War Department to the National Park Service on August 10, 1933. In the 1930s Fort Matanzas became a WPA project. A steel bulkhead and two groins were built along the water. The vaulted ceiling in the officer's quarters was rebuilt, and wooden stairways were constructed both into the fort and up to the officer's quarters.
Additional land on Anastasia Island was also acquired at this time, and a dock and visitor center/superintendent's house were constructed of coquina. For the first time, people without boats could get to the shorelne and look across the river at the historic fort.
Fort Matanzas National Monument now consists of nearly 300 acres-- the south end of Anastasia Island and most of Rattlesnake Island. Much of the land is preserved as natural habitat, but the National Park Service continues to preserve the historic fort as well. In 1999 the coquina chimney was reconstructed, and Fort Matanzas received two replica, iron 6-pounder cannon used in cannon firing demonstrations. In 2001 a new dock was constructed on the visitor center side, and a larger boat, Matanzas Queen III, was purchased in 2003.