The only evidence comes from early 20th century antiquarian writings, specifically O’Hanlon and O’Leary’s 1907 work, which makes a tantalising reference to what may have been a defensive structure at this location. Without archaeological excavation or further documentary evidence, the exact nature, date, and extent of this possible castle remain a mystery.

The site has a much longer and better documented religious history. St Dermot established an early Christian church here, though curiously the patron saint remembered by the community is St Comhdan (also known as Comgan), whose feast day falls on 27 February. This ecclesiastical settlement endured significant violence during the 11th century; Viking raiders plundered Killeshin and destroyed its oratory in 1041, and just 36 years later in 1077, the site was burnt again. These attacks reflect the vulnerability of Irish monastic settlements during this turbulent period, when both Norse raiders and competing Irish dynasties frequently targeted religious communities for their wealth and political significance.

The archaeological record at Killeshin, compiled by P. David Sweetman, Olive Alcock, and Bernie Moran for the Archaeological Inventory of County Laois in 1995, preserves these fragments of a complex past. Whilst the possible castle remains enigmatic, the documented history of the early church site reveals Killeshin as a place of considerable religious importance that survived repeated destruction to maintain its sacred associations through the centuries.