Square or rectangular baptismal fonts, vessels used to hold water for the sacrament of baptism, were common enough in England during the eleventh and twelfth centuries, but they never took hold in the same way in Ireland. Roughly three quarters of all known examples from the island are of English origin, which makes the Ballybacon font a rare domestic survivor of a form that was largely imported.

The font is carved from fine-grained granite and decorated on all four exterior sides. Three of those sides share the same composition: three large leaf motifs in relief, each flanked by a pair of triangles. The fourth side breaks the pattern with two flower-like rosettes, each composed of six petals, separated by two triangles set apex to apex. The exterior panels measure 0.57 metres by 0.53 metres, and the interior basin is 0.45 metres by 0.34 metres, with a flat bottom and a central drain. Cut into the underside is a large circular depression, 0.32 metres in diameter, which may indicate the font was once mounted on a stand or base. Cahil and Twohig, writing in 1976, examined the question of dating carefully. Rectangular fonts were fashionable in England from the eleventh century onwards, but scholar Helen Roe's work pointed toward a mid to late thirteenth-century date for this particular piece, placing it in the same period as a group of comparable fonts from Ossory, the medieval diocese centred on Kilkenny and Laois.

The font spent centuries outdoors in the grounds of the ruined medieval church at Ballybacon, in the nearby townland of Raheen. By 1975, concern about the effects of weathering on the carved stonework prompted its removal to the present church, which stands only a few hundred yards to the north-west of its original home. The move preserved the carving in reasonable condition, though it also shifted the font from its original ecclesiastical context into a working modern building, where it now sits as a quiet remnant of a thirteenth-century craft tradition that never quite found its footing on Irish soil.