The site first appears on Taylor’s 1783 Map of County Kildare, marked as ‘Terrils Ca. (castle) and Mills’, though by 1938 the Ordnance Survey maps show only the Temple Mills remaining. The castle’s history emerges from the Civil Survey of 1654, which records Mrs. Mabel Aylmer, described as an Irish Papist, as the owner of Tyrrell’s Mill and two acres of land valued at £16 yearly for rental purposes.

The survey provides a glimpse into the castle’s decline during the tumultuous 1640s. Where once a castle worth £100 stood proudly on those two acres in 1640, by 1654 it lay in ruins, its value reduced to a mere £5. This dramatic depreciation tells the story of Ireland’s Confederate Wars period, when many such fortified houses met their destruction. Though the castle had completely vanished by the early twentieth century, a fortunate survival exists in the form of a 1778 drawing by S. Walker, which depicts a narrow rectangular structure with a projecting corner tower; a typical design for Irish tower houses of the medieval and early modern periods.

Local historian Fitzgerald, writing between 1909 and 1911, confirmed that no physical remains of Tyrrell’s Castle survived into the twentieth century. The site’s transformation from defensive stronghold to industrial mill reflects broader changes in the Irish landscape, where military architecture gave way to commercial enterprise as the country moved from conflict to commerce. Today, visitors to Newtown will find no trace of the castle that once commanded this spot, but its memory persists in place names and historical records, a ghost of Kildare’s turbulent past.