The modern street plan of Dunmore, with its High Street and older plot boundaries still legible if you look, preserves the skeleton of an urban settlement that is considerably older than most people passing through it would suspect. A reference to the construction of a town wall here dates to as early as 1280, yet no trace of that wall survives above ground. The town has, in effect, grown over its own origins without entirely erasing them.

The borough was probably founded by Piers de Bermingham, who died in 1249, around the same time as the nearby castle, roughly a kilometre upstream on the Sinking River. The settlement is thought to have been concentrated on the north side of the river, at a fording point that made it strategically and commercially sensible. Two medieval monuments still survive in some form. The Augustinian friary, a religious house of the order founded in the thirteenth century and known across Ireland for their distinctive Gothic architecture, stands on Barrack Street. On the north side of Chapel Street, a site known locally as the Abbey is believed to mark the location of the medieval parish church, though what remains is fragmentary. Then there is a third feature, stranger and less explained: an earthwork on the eastern outskirts of the town, marked simply as "Mote" on the old Ordnance Survey six-inch maps. A mote, or motte, was typically the raised mound at the centre of an early Norman fortification, and this one sits on the edge of the town without a clear account of its relationship to the borough around it, quietly resisting an easy interpretation.