The Ross Errilly Friary (Irish: Mainistir Ros Oirialaigh, often anglicised in 18th & 19th century sources as Rosserelly) is a medieval Franciscan friary located about a mile to the northwest of Headford, County Galway, Ireland. It is a National Monument of Ireland and among the best-preserved medieval monastic sites in the country. Though usually referred to by locals as "Ross Abbey," this is not technically correct as the community never had an abbot.
The church and bell tower are to the south of a small but well preserved central cloister and domestic buildings are to the north. 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. The dormitories are on the upper levels. One unusual feature is a second courtyard or cloister, built to accommodate the friary's growing population.
Like many other abandoned Christian sites in Ireland, Ross Errilly has continued to be used as a burial ground by area residents. In addition to tombs that date from the friary's active period, many graves dating from the 18th through 20th centuries can be found inside the church walls. In some cases, tombstones comprise the floors of walkways and crawlspaces.