When researchers examined the drystone enclosure built by the Smyth family of Portlick Castle, they found an early Christian cross-slab, a carved stone marker of the kind associated with Ireland's early monastic period, built directly into the fabric of the wall. That stone is now in the National Museum of Ireland. The wall also incorporated architectural fragments of a late medieval building, most likely the remains of a church that once stood within the graveyard. What looks at first like a modest post-medieval burial enclosure turns out to be a palimpsest of occupation, each layer partly obscuring and partly preserving the one beneath it.

The site sits inside the bailey of a motte castle, the earthen platform and surrounding enclosure typical of Norman fortification introduced to Ireland from the twelfth century onward. That motte castle may itself have been raised on the footprint of a much earlier Christian ecclesiastical enclosure, with the curving ditch to the north and east possibly tracing the outline of the original boundary. The 1838 Ordnance Survey six-inch map records the area as a roughly D-shaped graveyard, approximately 58 metres north to south and 66 metres east to west, set within a field called the Church Park. By the revised 1914 edition, a smaller rectangular burial ground belonging to the Smyth family is shown sitting within the centre of that larger space. Research by Reilly in 2016 clarified that what the later maps depict as a wall enclosing the whole site is actually a bank of earth and stone, roughly oval in shape, enclosing an area of around 70 metres east to west by 60 metres north to south. The same work uncovered fragments of two rotary quern stones, used in earlier centuries for grinding grain, both of red sandstone conglomerate, found near the earthen bank to the south-west. A possible bullaun stone, a basin-shaped hollow cut into rock and often associated with early ecclesiastical sites, lies around 120 metres to the south. The Smyth family connection to the land dates to 1703, when Reverend Robert Smyth of Dublin purchased 190 acres of the Portlick Castle estate, land that had previously been part of the confiscated Dillon estate and had passed through the hands of Thomas Keightly, a member of the Privy Council of Ireland, before being sold to a Dublin merchant named William Palmer.