From the Civil War Florida website by Dale Cox.
I'd never heard of a fort by the lighthouse on the St, Marks River in Florida. I wasn't even sure where the river was. It flows into the Gulf of Mexico near the eastern edge of the Florida Panhandle.
The Confederate battery/fort that the Union ships destroyed in the last post was rectangular in shape named Fort Williams and so constructed as to defend the mouth of the St. Marks River.
It was already complete by June 1861 when the USS Mohawk arrived to enforce Lincoln's blockade. Confederates occupied it until the summer of 1862 when it was abandoned in favor of a new fortification built upriver on the ruins of the old Spanish fort of San Marcos de Apaliche.
The fort was burned by Union sailors from the USS Tahoma and USS Somerset.
The listing in the Civil War Naval Chronology that I used for the last post made it sound like there was an actual battle that took place at Fort Williams, but this makes it seem like it was nothing more than the occupying of abandoned works.