The castle occupies a low rise in undulating pastureland, its mound measuring about 10 metres east to west, likely formed by centuries of collapsed masonry. Just 50 metres upslope lies an associated church, whilst earthworks scatter the surrounding field, hinting at the broader settlement that once existed here.

Historical records paint a picture of the castle's decline over centuries. The Down Survey map from the 17th century depicts the structure, whilst the Civil Survey of 1654-6 provides more detail, noting it belonged to one Edmond Mocler, described as an 'Irish Papist' of Maginstown. By this time, the surveyors recorded it as 'an old small Castle ruined', with another contemporary account dismissively referring to it as 'Magonstowne a stump of a Castle'. These descriptions suggest the fortification was already in considerable decay by the mid-1600s, perhaps a casualty of the Cromwellian conquest or earlier conflicts.

Today, only fragments of the limestone rubble structure survive, with the north and south walls partially standing; the southern wall reaches 5.5 metres in height and features a projecting corbel course about 2 metres up its external face. The interior measures just 2.45 metres north to south, indicating this was likely a modest tower house rather than a grand fortress. When surveyed by the Ordnance Survey in the 19th century, investigators noted traces of a western wall and what appeared to be cut stones from a doorway on the northern side, along with evidence of a window that widened internally, typical of defensive architecture. They also observed foundation traces about 34 yards northwest of the main structure, suggesting outbuildings that once served the castle's inhabitants.