Gothic script on the 1840 Ordnance Survey map marks this site as a castle, whilst the 1657 Down Survey shows two castellated buildings in the area where Lynn church and Lynn House now stand. These structures likely represent the remains of both Lynn Castle and the medieval church, though centuries of rebuilding have made it difficult to determine exactly what belonged to which building. When Ordnance Survey officials examined the site in the 19th century, they found themselves trying to untangle old walls from new, noting fragments of ancient construction embedded within more recent masonry, including walls barely 18 to 20 inches thick that seemed too insubstantial to be castle fortifications.

The most visible remnant today is an archway behind the early 19th century Lynn House, consisting of two sections of rubble wall about 2 metres long and rising nearly 4 metres high. The inner faces reveal what was once a doorway, though the arch itself appears to be 18th or 19th century brick construction, possibly built atop medieval foundations. This entrance may have originally led into a bawn, a fortified courtyard typical of Irish castles, approximately 2 metres wide. The 1840 map suggests the castle building stood in the western corner of a quadrangular enclosure, with Lynn House later built into the southeast angle of this medieval bawn during the 18th or 19th century, effectively transforming the old defensive courtyard into a domestic one.

By 1910, the Ordnance Survey had revised their maps to label the site as a ‘Monastery (in Ruins)’ rather than a castle, reflecting ongoing confusion about the site’s original purpose. A 1983 archaeological visit found no evidence to support the monastery theory, though the surveyor noted that adjoining walls and outbuildings appeared to date from the late 18th or 19th centuries, with no other visible medieval features remaining. The site remains an intriguing puzzle; the original medieval castle may have been completely levelled, its stones recycled into Lynn House, whilst the bawn walls were adapted to serve as a fashionable Georgian courtyard, leaving only tantalising fragments of a once formidable fortress.