The site sits on level ground with clear views to a motte about 150 metres to the west, whilst a church and graveyard lie just 35 metres to the east-northeast; a spatial arrangement that suggests this was once an important defensive and administrative centre. Today, only the ghost of the structure survives: an L-shaped corner formed by two walls built from thin, coursed flagstones, standing about 3.5 metres at their highest point. The walls, nearly two metres thick, show the characteristic gentle batter at their base that was common in medieval Irish fortifications.

Further investigation reveals additional clues about the castle's original extent. Some 13.5 metres northeast of the surviving corner, another L-shaped mass of mortared masonry marks what was likely the building's north corner, though it now stands less than a metre high and has lost its facing stones. Intriguingly, a narrow stone passageway with a pointed arch vault has been discovered nearby; this subterranean feature, measuring just 1.5 metres long and barely wide enough for a person to pass through, appears to be a later addition to the site. The 1939 Ordnance Survey map mistakenly identified this as a souterrain, though its construction style suggests otherwise.

The castle may have once stood within a bawn, or fortified enclosure, though evidence for this defensive perimeter is now largely invisible. Traces of a surrounding fosse, or defensive ditch, were documented in 1986, and whilst these features can no longer be clearly seen at ground level, a subtle scarp about 80 centimetres high may still mark the line of these former defences. The proximity to both religious and military sites, combined with the substantial construction of the surviving walls, points to Lackagh Castle having been an important stronghold in medieval Kildare, possibly associated with the early castle believed to have existed in this location.