A baptismal font is the vessel used for the Christian rite of baptism, typically a permanent fixture at the entrance to a church, and this one is a modest but precisely described object: octagonal in shape, 0.31 metres high, with a bowl diameter of 0.64 metres and a central drainage hole. Finding a medieval font repurposed as a garden feature is unusual enough, but this particular object carries an additional layer of ambiguity, having been separated from the church it belonged to twice over, and by two quite different hands.

The font originally stood in the medieval church of Knock Killua, dedicated to St. Lonán, which lies 3.2 kilometres to the north-east of Ballinlough Castle. At some point before the 1930s, it was removed from that site and brought to the castle's estate, and around that same period it was placed in the walled garden where it stands today. When the antiquarian Oliver Davies visited the Knock Killua graveyard in 1940, he noted only scattered cut stones and what he described as part of the basin of an octagonal font, fragmentary remains that may well represent what was left behind after the font itself had already been taken. The owner of Ballinlough Castle, when later consulted, believed the font had been removed from a medieval church on the castle's own estate, suggesting some confusion had grown up around its origins. The trail of evidence, pieced together across decades, points back to St. Lonán's church as the font's true provenance.

The font at Ballinlough Castle is not publicly accessible in any straightforward sense, sitting as it does within a private walled garden. The ruins of the medieval church at Knock Killua, where those fragmentary cut stones were observed, represent the original context, though what remains there now is unclear. The interest lies less in any single surviving object than in the gap between them, a medieval artefact displaced, misattributed, and only partially accounted for across the better part of a century.