The castle’s history is marked by violence and intrigue, most notably the brutal murder recorded in 1541 by the Annals of the Four Masters. Ferganainm O’Carroll, blind and elderly, was treacherously killed by his own kinsmen, Teige O’Carroll and John O’Molloy, within the castle walls. Despite his blindness and age, the old chieftain fought so fiercely against his attackers that he earned lasting fame for his valour; twelve of his loyal men died alongside him in the bloody assault.

The castle held secrets beyond its violent history. According to nineteenth century accounts, it contained a mysterious room called the ‘Chamber Arrigett’, believed to have served as a hidden treasury where the O’Carrolls stored their wealth. This wasn’t merely speculation; when Sir William Parsons of Birr and Captain William Paisley attacked the castle in 1639, they discovered not only a cache of muskets and pikes but also a concealed chamber that had apparently been used for minting counterfeit coins in earlier times.

By the seventeenth century, the Down Survey maps show Clonlisk Castle as a tall, rectangular structure accompanied by a smaller house and a watermill on the nearby stream’s south bank. The 1641 terrier describes it as part of an Irish settlement complete with castle, mill, and the characteristic ‘Irishtowne’. At that time, the property belonged to John Carroll, an Irish Catholic landowner, representing one of the last generations of the O’Carroll dynasty to hold their ancestral seat before it eventually disappeared from the landscape, leaving only historical records and archaeological traces of its turbulent past.