Within the larger enclosure, a smaller rectangular burial ground belonging to the Smyth family of Portlick Castle sits at its centre, walled in drystone and incorporating architectural fragments from a late medieval building, possibly a church that once stood on the same ground. That wall, built to mark the resting place of one post-medieval family, was found to contain an early Christian cross-slab, a carved stone likely dating from the early medieval period, which has since been removed to the National Museum of Ireland. Fragments of two rotary quern stones, the upper and lower halves of a hand-grinding mill both made of red sandstone conglomerate, were also found lying near the enclosing earthen bank to the south-west, suggesting repeated and varied human use of this ground across many centuries.

The site carries a remarkable density of overlapping histories. The graveyard itself appears to have been established within the bailey of a motte castle, the earthen platform and enclosure type introduced by the Normans, which in turn may have been constructed on top of an earlier early Christian ecclesiastical enclosure. A church building, now completely levelled, may also have stood inside the graveyard at some point. The field in which all of this sits was recorded on the 1838 Ordnance Survey six-inch map as the "Church Park", a name that preserves the memory of something ecclesiastical even as the physical evidence was disappearing. The estate itself passed through several hands after confiscation from the Dillon family; Thomas Keightly, a member of the Privy Council of Ireland, received the 356-acre Portlick estate before selling on portions of the land. In 1703, Reverend Robert Smyth of Dublin purchased 190 acres including Portlick Castle, and it is his family whose private burial enclosure came to occupy the heart of the older graveyard, absorbing stonework from the very building it replaced.