What was once a rectangular fortress, believed to have been constructed by the D'Cantillon family, has been reduced to little more than a mound of rubble measuring 25 metres north to south, 46 metres east to west, and averaging just 1.7 metres in height. The castle's current state offers few clues to its past grandeur, making it a peculiar puzzle for history enthusiasts and archaeologists alike.

When antiquarian John O'Donovan surveyed the site in 1841, he documented walls that still stood an impressive 20 feet high, roughly 6 metres, and clearly defined the castle's rectangular footprint. However, sometime between then and now, practicality won over preservation; the castle's stones were systematically removed and repurposed for building a track and shed that now sit immediately north of the original site. This act of architectural recycling, whilst common in rural Ireland, has left Rathmorrell Castle as little more than a ghost of its former self.

Today, visitors to the site will find themselves standing before what appears to be an unremarkable hillock of stones, with no visible indication of the defensive structure that once commanded this spot. The transformation from standing walls to scattered rubble serves as a sobering reminder of how quickly built heritage can disappear when left unprotected. Despite its diminished state, Rathmorrell Castle remains catalogued in the North Kerry Archaeological Survey, a testament to its historical significance even in near total ruin.