The last sentence on the plaque: It appears that in the War of 1812, Fort Pickering was built on the Fort Tonyn site. In a search for information about Fort Pickering, three forts of that name were found; one in Georgia, another in Massachusetts and a third in Tennessee.
This site believes the information on the plaque above is in error:
NOTE: State of Georgia Historic Marker for Point Peter - Fort Tonyn, located in St. Marys. Information appears to be in error. British Fort Tonyn (1776) was located in East Florida, one mile east of King's Ferry. Fort Pickering (1814) was located further upriver at Coleraine.
This August 17, 1796, letter from the Papers of the War Department stated that Fort Washington at Point Peter [was] still not garrisoned.