According to Cope (The Modern Antiquarian – page 296), Hirfaen Gwyddog has a written history dating back to the 8th Century CE when it was called behet hirmain in the Book of Chad. In a 12th Century CE charter it was referred to as Hyrvaen Gudauc, and in 1633 CE it was called Hirvaen gwyddoc by Edward Lhuyd.
Hirfaen Gwyddog stands on the county boundary between Ceredigion (historically known as Cardiganshire) and Carmarthenshire. It also marks the point where the land of three farms meets. In his book Mysterious Wales Chris Barber describes the stone as ‘the tallest standing stone in Dyfed’. I’m not sure whether this is true or not, but at 4.8 meters it must come close.