According to the Civil Survey of 1654-56, Major General Sir Hardress Waller's estate here boasted a castle, sixteen cottages, a pigeon house, an orchard, and a weir seat along the River Shannon. The castle itself, which stood near what would later become Castletown Manor house, played a dramatic role in the Confederate Wars when General Patrick Purcell besieged Sir Hardress Waller there for six weeks in 1642. Waller eventually surrendered, not from military defeat but from a rather mundane yet critical shortage; the defenders had run out of water.

The siege account provides remarkable detail about the castle's defences and contents. Waller described a substantial stone stable building with fine timber work, and mentioned that repairs to the castle and its barbican had cost £300, a considerable sum for the period. His inventory included twenty muskets, fowling pieces, callivers and a harquebush, painting a picture of a well-armed household prepared for troubled times. The presence of a barbican, essentially a fortified gatehouse, suggests the castle was protected by a bawn or walled courtyard, within which the stable, orchard and pigeon house were likely situated. This defensive arrangement was typical of plantation castles in Ireland, designed to protect both the main residence and its supporting structures.

Sir Hardress Waller's fortunes took a dramatic turn when he signed King Charles I's death warrant as one of the regicides, leading to the forfeiture of his estates after the Restoration. Though the lands were granted to Sir Henry Ingoldsby, Waller's descendants somehow managed to retain possession. The original castle gave way to Castletown Manor house, built on or near the same site, which stood until its demolition in 1935. Today, no visible remains survive of either the castle that witnessed the 1642 siege or the manor house that replaced it, leaving only historical records to tell the tale of this once-fortified estate along the Shannon.