It is a compact octagonal piece of limestone, just 31 centimetres high with a bowl diameter of 64 centimetres, and it retains a central drainage hole, the practical detail that once allowed water to be cleared after baptisms. A font of this kind was the fixed centrepiece of parish religious life, the vessel in which infants were received into the church, and its presence in a private garden speaks to a long and somewhat tangled journey.

The font originally belonged to the medieval church of Knock Killua, dedicated to St. Lonán, which stood some 3.2 kilometres to the northeast of the castle. At some point, probably in the 1930s, it was moved to its present position in the walled garden, roughly 175 metres from the main castle building. The castle's owner indicated that the font had at some earlier stage been brought from the Knock Killua church site to the castle estate, though the precise circumstances of that earlier removal are not recorded. The estate surrounding Ballinlough Castle, now largely given over to a golf course, was once a more enclosed world of landscaped grounds, and garden features with ecclesiastical origins were not unusual in such settings, where carved stonework was sometimes gathered almost as ornament.