The old church, said to have been known as the “Church of the Fairy Palace”, is situated near Monkstown Castle on the side of the Glen. It is thought to have been the last retreat of the Benedictine monks who established a monastery in Monkstown. It was subsequently appropriated and repaired by the Archdeacon family of Monkstown castle for use as a domestic chapel. Some say that there is an underground tunnel from the castle to the old church but, if there is, it is not to be seen today. John Archdeacon claimed to have built the church. This is not true, but he probably did renovate it.
The old church was small, measuring about 10 metres by 5 metres. Now only the gable ends and part of the side walls stand. It was built with sandstone from a quarry in Raffeen and bonded with lime mortar. The doorway, formerly arched, is near the west end of the south wall. The window near the east end of the south wall has a flat-headed light, while that in the centre of the east gable has an ogee-headed light (an arch formed by two S-shaped curves meeting at a point). By 1700, the church was described as having “the roof up but the timbers beginning to decay”.
There are graves inside and outside the old church, most of which date from the 18th century. The oldest grave in the church and occupying the place of honour on the gospel side of the altar is that of John Calanane, who died in 1710. It is said that there is another graveyard dating from the 12th century underneath that which is visible today.
John Archdeacon and his wife, Anastasia Archdeacon Gould, were buried in the old Monkstown graveyard just yards from their former home. Their altar tombs can be seen along the south wall of the church. Their son, William, and his wife Anastatia Skiddy are also buried there. The inscriptions on their tombs are in Latin.
While Sir John Newman lived at the castle, he had the graveyard closed as it was too small and quite stony. It is known that smugglers occupied the graveyard during the 18th and 19th century.