It is something quieter than that: a sunken rectangular outline in the turf, a grass-covered trace of walls reduced to their foundations, sitting at the highest point of a roughly circular raised graveyard. The church itself collapsed sometime between 1615 and 1630, and was never rebuilt. What remains is a shallow depression, about 22 metres east to west and just under 11 metres north to south, with wall foundations surviving to no more than half a metre in places. A large mausoleum belonging to one Edward Byrne was subsequently built over the eastern end of what was probably the chancel, neatly obscuring the most liturgically significant part of the plan.

The site traces its origins to a figure named Mosaccra, an abbot recorded in the Martyrology of Donegal as founder of Tigh Sacra, meaning the house of Sacra, from which the place name Saggart derives. He is noted as having attended the Synod of Flan Fabhla, Archbishop of Armagh, in 697. After the Anglo-Norman invasion, the district became one of four royal manors in County Dublin, and the church passed into the administrative orbit of St Patrick's Cathedral, Dublin, as a prebend, meaning it was held by a cathedral canon whose income derived partly from the revenues of this parish. By 1275 it was valued at £20 per annum; the 1302 to 1307 Ecclesiastical Taxation placed it at £10 with tithes of 20 shillings. The chapels of Newtown and Symon-Tallaght both served as daughter chapels under its authority. A Royal Visitation of 1615 found the church and chancel in good condition, the Latin record noting it was furnished with books, and the prebend was served by one Roger Danby, described as a Master of Arts and a very sufficient preacher. By 1630, Archbishop Bulkeley's visitation recorded a very different picture: the church had fallen down, about thirty parishioners were travelling to Rathcoole to hear services, and the rest, the record notes plainly, were recusants.

The graveyard remains in use and is accessible from the village. The circular form of the enclosure, defined to the east by a ditch and a curving stone wall, is most legible from within the site itself, where the raised ground gives a faint but real sense of the original ecclesiastical boundary. The church foundations are largely covered by sod and have been further disturbed by centuries of burials, but the sunken outline of the nave and the shorter chancel to the east are still readable underfoot if you walk the perimeter carefully. A rectangular foundation to the south, abutting the church wall, appears to have been a separate structure. The Byrne mausoleum dominates the eastern end and is the most visible above-ground element on the site.