It is modest in size, roughly 65 by 47 centimetres, set within a chamfered surround and carved in raised relief. Above the text sit the initials IHS, a cross, and a monogram for Ave Maria, the standard devotional shorthand of Counter-Reformation Catholic piety. What lifts this particular slab out of the ordinary is the name it preserves: one of the two men credited as founders of the chapel is Dr Geoffrey Keating, the seventeenth-century priest, poet, and historian whose Irish-language history of Ireland, "Foras Feasa ar Éirinn", became one of the most widely copied manuscripts in the country.

The inscription, composed in contracted Latin and dated 1644, asks prayers for the souls of Father Eoghan O'Duffy, vicar of Tubbrid, and of Keating himself, described here as "Domini Doctoris Galfridii Keating", the Latinised form of his name. The full text, once expanded from its contracted form, translates as: "Pray for the souls of Father Eoghan O'Duffy vicar of Tubbrid and Dr Geoffrey Keating the founders of this chapel, as likewise for all other, clergy as well as laity whose bodies rest in the same chapel, AD 1644." The plaque attracted enough interest to be sketched twice in later centuries, once in the Ordnance Survey Letters compiled by O'Flanagan in 1930, and once by the nineteenth-century artist and geologist George Victor du Noyer, whose careful drawings of antiquities are themselves now historical documents. The chapel sits at the eastern end of the graveyard, its west gable still carrying the memorial above its doorway, quietly marking a place associated with one of the most significant figures in early modern Irish literary culture.