The field where it once stood has been completely reclaimed, ploughed and reseeded with grass, leaving no trace of the medieval fortification that once guarded this strategic river crossing. The old Mill Road, which appears on the 1840 Ordnance Survey map leading down to this spot, once brought travellers to a crossing point marked by stepping stones that can still be seen in the river. Though the current landowner reports no local memory of a castle here, the area is still known as ‘the island’, a name that hints at its unusual geography.

The 1657 Down Survey maps reveal the castle’s clever defensive position; a channel had been cut between the two rivers, creating an artificial island on which Lismullane Castle stood. This low, battlemented tower appears to have been built by the Bourke family, who held the lands for generations. Historical records show various branches of the family in possession throughout the 16th and 17th centuries, with the 1540 Rental noting that Sliocht Edmond Mac William held Lios Mothlán, whilst Maoilre Burk held Lios Mothlán beág. By 1583, W. Bourke controlled the castle, and in 1623 it had passed to Richard fitz Thomas Bourke.

The Down Survey terrier lists several proprietors of the 290 acres in Clonkeen parish that included the castle; Walter Bourke of Killownane, David Barry, Connor Clancy, Richard Bourke and Donough McConnor. By the time of the 1840 Ordnance Survey, only a cluster of dwellings remained at the site, along with the mill that gave the old road its name. Writing in 1907, Reverend Seymour noted that whilst the site was no longer marked on contemporary maps, local knowledge still placed the Bourke castle precisely where the Slievemohera River (another name for the Killeengarriff) meets the Mulkear.