The 1838 Ordnance Survey six-inch map labels the building now known as Desmond Hall as 'Church (in ruins)', with the Church of Ireland building sitting immediately to its north. Somewhere in that tight cluster of old stonework, a parish church once served the town, but the ground has not given up a clean answer.

The antiquary Thomas Johnson Westropp, writing in 1904 and 1905, noted that there were in fact two churches associated with Newcastle West. One, at Churchtown, stood near St. David's Well and appears in seventeenth-century sources by that association. The other is the one whose precise location remains disputed. Westropp recorded that a church was destroyed in the early fourteenth century, though whether this was the building close to the castle or the one at Churchtown is unclear. By 1401, the Churchtown church was apparently in good condition and dedicated to St. David. The Church of Ireland building that replaced whichever church occupied the castle demesne site was built in 1777, with the site granted by W., Viscount Courtenay. An earlier ecclesiastical order, dated 1775, had directed the union of the churches of Newcastle and Monagay under Newcastle.

For those exploring the demesne today, the physical traces of the earlier church survive in fragmentary but tangible form. A reused window head, with cusps and moulding, has been set over a well in the castle garden, and further architectural fragments can be found around an ornamental pond near the castle wall. These pieces are almost certainly salvage from an earlier ecclesiastical structure, though whether that structure was the medieval parish church itself remains an open question. The bawn, which refers to the defensive enclosure surrounding a castle, is the area where some of these fragments are concentrated. The demesne is in the town centre of Newcastle West, and the juxtaposition of Desmond Hall, the later church, and these scattered stonework details makes for a quietly layered piece of ground.