The castle appears as a rectangular structure on the 1913 Ordnance Survey map, where it's clearly marked as being in ruins. Today, what remains is a modest rectangular area measuring roughly 8 metres northwest to southeast and 6 metres northeast to southwest, defined by low, grass-covered walls that stand between 2 and 2.5 metres high. The interior has partially filled with collapsed rubble over the centuries, giving only hints of its former layout.

The castle doesn't stand alone; low banks and wall footings in the immediate area trace the outlines of buildings that once adjoined the main structure. These remnants suggest a more extensive medieval complex than the castle ruins alone might indicate. Larger enclosures extend outward from the castle on all sides, visible as earthworks that mark where defensive walls or agricultural boundaries once stood.

The site's features are particularly clear in oblique aerial photographs taken in July 1966 and July 1969, which reveal the full extent of the earthworks and their relationship to the castle ruins. These images, captured before modern agricultural practices might have disturbed the ground further, show how Oldtown Castle formed the centre of a larger medieval settlement, its surviving walls and earthworks offering a glimpse into Westmeath's medieval past.