The town’s history stretches back to the 6th century when St Brendan founded a monastery here, which grew into one of the most prestigious religious foundations in Ireland and became part of St Columcille’s influential federation of churches. Its strategic location at the crossroads of four provinces; Munster, Meath, Leinster and Connacht; made it a natural meeting place for royalty and clergy alike, hosting important synods in 697 and 1174 AD.

The Anglo-Normans arrived around 1207, building a castle and establishing a settlement that lasted roughly a century before the O’Carrolls of Ely reclaimed the area by the mid-14th century. Their stronghold, known as the Black Castle, served as the principal seat of the ruling branch of the dynasty until 1594, when it was sold to Butler of Ormond. The landscape changed dramatically in 1621 when Laurence Parsons acquired the lands as part of the Plantation of Ely O’Carroll, renaming the settlement Parsonstown and constructing a new castle that remains the Parsons family residence today.

The original Black Castle met its end in 1778 when it was demolished to make way for the manicured lawns and parkland surrounding Birr Castle. Local tradition holds that the castle may have been built atop an earlier Anglo-Norman motte, though both structures were thoroughly levelled by the 18th-century residents. Today, only the faintest traces of the motte remain visible in an area overlooking the Camcor River, west of Birr Castle, leaving visitors to imagine the medieval fortress that once commanded this strategic river crossing.