The structure dates back to at least the 13th century, with architectural analysis suggesting it began life as a hall house measuring 16.8 metres by 8.2 metres. Over time, this original building was transformed into a more defensive structure, with the addition of flanker towers on the eastern corners and various internal modifications including vaulted floors and thick crosswalls. The southern tower measures roughly 6 metres by 2.6 metres internally, whilst the court spans 9.75 metres by 6 metres, with walls reaching heights of approximately 10.6 metres and thickness of about 1 metre.

The castle’s military significance became dramatically apparent during the Confederate Wars of the 1640s. In January 1642, Confederate forces under Edy Lacy of Bruree besieged Kilfinny, though they were initially repelled by just ten musketeers positioned on a windmill. General Purcell subsequently arrived with reinforcements, capturing the mill and barns before being driven off when the defenders burnt the buildings during a bold sally. The siege intensified when Richard Stephenson, the sheriff, led an assault but was shot dead, and attempts to breach the walls using ‘sows’ (mobile protective shelters) failed when these siege engines were pierced through. Despite the loose blockade, Lady Dowdall managed to relieve nearby Croom Castle five times from Kilfinny. The castle finally fell when Confederate forces, now equipped with heavy artillery from the recently surrendered Limerick Castle, compelled Lady Dowdall to surrender after just three cannon shots, though Lord Inchiquin ensured her safe conduct.

By the mid-17th century, the Civil Survey of 1654-56 recorded Lieutenant Colonel William Piggott as owner of Kilfinny, which then included not just the castle but also an orchard and a mill seat. The property later passed to the FitzGerald family, with Gerott FitzGerald holding it in 1655. Local tradition associates the castle with the McEniry family, though documentary evidence points to various owners throughout its history. The site underwent further modifications in the 17th century, with a new range added adjoining the southeast flanker tower, demonstrating how these medieval fortifications continued to evolve and serve as residences well into the early modern period.