Built reportedly in the late 16th century by Edward Goff, the castle passed into the hands of Patrick Geogh of Kilmanahan around 1640, reflecting the complex patterns of land ownership that characterised this period of Irish history. Today, only fragments of this once substantial residence survive, offering tantalising glimpses into its original grandeur.

The surviving architecture provides intriguing clues about the castle’s original layout. A 4.75-metre section of the north wall still stands, complete with a spiral staircase that would have connected the building’s different levels. The adjacent west wall preserves fragments of two doorways, suggesting this may have been an internal wall within a much larger structure. Archaeological evidence indicates the original house was oriented east to west, with what appears to have been a services tower at the eastern end; a typical arrangement for substantial houses of this period where kitchens and storage areas were often separated from the main living quarters.

The castle doesn’t stand in isolation within the landscape. Local tradition holds that a graveyard site exists about 180 metres to the south, whilst an earthwork site sits immediately adjacent to the north, suggesting Greenan Castle was part of a broader settlement pattern in the area. These associated features hint at the castle’s role as a focal point for the surrounding community, serving not just as a private residence but as part of a larger social and economic network that shaped this corner of County Waterford for centuries.