Archaeologists Heather Cline and Mary Socci say the 900-square-foot house was owned by Scottish immigrant William McKimmy and was built about 1790.
That would mean the home predates Thomas Jefferson's Poplar Forest. That home was built in the 1820s near Lynchburg, Va., and is considered to be the first octagonal house in the U.S.
The director of archaeological restoration at Poplar Forest says he questions whether the find in South Carolina is a full-size home.