Amongst these are a kitchen (equipped with an oven and a water tank for live fish), a bake house, and a refectory or dining area.

Both Luke Wadding and the Four Masters (who refer to Ross Errilly in their Annals as Ros-Oirbhealagh) record that the abbey was founded in 1351, but this date has been called into question by numerous historians.

In any case, it is clear from the architectural evidence that any religious building that may have been on the site prior to that time was greatly expanded during the 15th century.

In 1604, Ulick Burke, 3rd Earl of Clanrickarde, continuing to honour the de Burgh tradition of supporting Ross Errilly, financed the rehabilitation and reoccupation of the monastery by the Franciscans.

Daniel apparently complied with the order, but sent advance word to the residents of Ross Errilly and advised them to evacuate the abbey's most precious items.

Burke and the monks brought the survivors back to the Headford area and obtained shelter for them among the townspeople until safe passage to England could be arranged.

The Irish campaigns of Oliver Cromwell brought an end to this era of English tolerance of the Catholic Church in Ireland.

For a few nervous years, Ross Errilly served as an informal refugee shelter for Catholic clergy who had been flushed out of other parts of Ireland by Cromwell's forces.

The 140 Franciscans living there had fled a few hours earlier, but the soldiers ransacked the grounds, destroying crosses and other religious iconography and even defiling tombs in search of loot.

The property was now owned by Lord St. George, a local noble, who picked up where the Clanrickardes had left off and secretly patronised the abbey.

The monks built cabins of wood and stone on a small island in the Black River, about one mile (1.6 km) downstream from the abbey.

In 1789, a Henry Lynch of Ballycurrin cheaply leased 16 acres (65,000 m2) to the dispossessed monks at the foot of a hill in the townland of Kilroe, near Headford.

"[6] Geographer Samuel Lewis noted the continued decay in 1837, writing that the abbey was "partially covered in ivy" and that the roof had collapsed in 1812.

He also credited a nearby resident, Oliver Burke, with some early efforts to preserve the site by "removing obstructions from between the mullions of the beautiful windows" and making "repairs to the tower, thereby rendering it accessible to the top.