Going forward I would have some concerns about this site being exposed to vandalism because of the increase in population in the immediate vicinity.
The last time I visited the church was effectively isolated close to the end of a remote tree lined country lane and access to the grounds was blocked by metal barriers. There was evidence that a major construction had stalled or even abandoned. Today, it was very different as you can see from this series of photographs.
Tully Church lies in Laughanstown (variously spelled Lehaunestown, Lehaunstown). It is located in Dún Laoghaire-Rathdown, 500 m south-southeast of Laughanston Luas stop (Green Line).
The original church structure dates to the 6th–9th centuries AD. One ancient name is Telach-na-nun ecspop (Tullow of the bishops) and it must have been an important venue if bishops met there. There is a legend that seven bishops started out from there to visit St Brigid at Kildare. Elsewhere these bishops are mentioned as the "Seven Bishops of Cabinteely" (Alice Curtayne, Saint Brigid of Ireland)
In 1179 the Church was granted to the Priory of The Holy Spirit.
The chancel, which is wider than the nave, was added in the late 12th or early 13th century by the Normans. The unusually larger chancel was added to the nave during the early 13th century and has a rounded arch and two rounded headed east windows. The nave dates to the 13th century.
The church was in use up to about 1615. It came under the authority of Christ Church Cathedral, Dublin who supplied clergy to keep it going. It was reported to be in good condition when inspected in 1615, but according to a report in 1630 had been badly damaged in recent storms. After that it was abandoned and fell into ruin.