After the Civil War, the Federal government had little use for the old fort other than as a lighthouse and depot. The guns were left in place (some are still there) and, in general, it was left to decay. By 1890, it was so bad, the fort was sealed, filled with sand and prepared for use as a lighthouse foundation.
In 1897, there was a proposal to use it as a nursing home for Union veterans, but that never came to be. No weapons were added during the Spanish-American War or World War I as happened at so many old coastal fortifications. (In Charleston Harbor, guns were added at Fort Sumter.)
The US Army Corps of Engineers did use it as a base for harbor improvement projects.
On October 15, 1924, President Woodrow Wilson proclaimed the Castle Pinckney National Monument and placed it under War Department administration and in 1933 it was transferred to the National Park Service.
HOT POTATO
The NPS didn't have any plans for it and in 1951, Congress abolished the status and it was transferred to the US Army Corps of Engineers, but they didn't want it and declared it surplus property. A Congressional mandate turned it over to dispose of it.
Today, it is owned by the South Carolina State Ports Authority. In 1969, they had sold it to the Sons of Confederate Veterans who intended to restore the fort, erect a museum and build an up-scale restaurant, but that fell through.
In 1970, it was listed on the National register of Historic Places, but not much has been done since then.
Today, it's still there, and boat guides talk about it. You can't land on the island without permission and very few have been on it.
Sad to See a Historical Structure Go By the Way Like This. --Old B-Runner