It appears on a town plan drawn up in 1691, a small institutional mark on an early map of what was then still a relatively young planned settlement. No trace of the building survives above ground, and its precise footprint has never been pinned down, which gives it an odd presence in the historical record: documented but unlocated, known but vanished.

The gaol's appearance on Richard's 1691 plan places it in the context of a town that had only been taking its current shape for around seventy years. Birr had a far longer history behind it, of course. St Brendan reputedly founded a monastery here in the sixth century, and the settlement grew into one of the more significant foundations within St Columcille's federation of churches, hosting synods in AD 697 and 1174 at which kings and churchmen gathered from across the surrounding provinces. Anglo-Norman lords held a castle here from at least 1207, and by the mid-fourteenth century the O'Carrolls of Ely had made their 'Black Castle' one of the principal seats of their dynasty, retaining it until its sale to the Butler of Ormond in 1594. The town as a functioning urban settlement, however, really began with the Plantation of Ely O'Carroll in 1621, when Laurence Parsons was granted the lands and 'castle and fortilage' of Birr and set about creating the manor of Parsonstown. He secured a Tuesday market and two annual fairs that same year, added a Saturday market and two more fairs in 1627, and by 1626 the town already had a Free School. A market cross was erected around 1625. Mills of several kinds were operating along the local waterways. The gaol marked on the 1691 plan fits neatly into this picture of a plantation town acquiring the full apparatus of civic order, commerce, and control within a single lifetime.