The castle appears on the Down Survey maps from 1655 to 1656, those remarkably detailed cartographic records created by William Petty following the Cromwellian conquest of Ireland. These maps were commissioned to document land ownership across the country, providing a snapshot of the Irish landscape in the mid-17th century, including castles, churches, and settlements that have since vanished.

The absence of visible remains suggests the castle was likely demolished or fell into ruin sometime after the Down Survey was completed. Many Irish castles met similar fates during this turbulent period; some were deliberately slighted during the Cromwellian campaigns, whilst others were simply abandoned as the old Gaelic and Old English aristocracy lost their lands. The fact that Bellmount Castle warranted inclusion on the Down Survey maps indicates it was still a significant structure in the 1650s, important enough to serve as a landmark for surveyors mapping the redistribution of confiscated estates.

Today, the site serves as a reminder of how much of Ireland’s built heritage exists only in historical records. Without archaeological excavation, we can only speculate about the castle’s original size, layout, or who built it. The Down Survey maps, now digitised and freely available online, remain our best evidence that a castle once commanded this spot in the Offaly countryside, part of a network of fortifications that once dotted the Irish midlands.