A church commemorating St. Illand who flourished in 540 A.D. stood in this townland. Illand is said to have been a descendent of Niall of the Nine Hostages. The monks had a school here where the sacred scriptures were taught and where secular learning was cultivated. A cemetery developed around the church. Rev. John O'Hanlon visited the scene in 1888 and found the church in ruins. The stone had been used to build a wall around the graveyard. Bishop Ussher in his Britannicarum Ecclesiarum Antiquitates states the church was in ruins in 1622. A Roman document says that Fr. Donal Molloy was in charge of Rathlihen church in 1636. Several documents report that a statue of St. Illand with a mitre on his head and a crozier in hand was to be seen at Rathlion. But by 1838, there was no evidence of it or information to be had about it.
On 17 March 1985, Mrs. Anne Daly went for a stroll which took her past Rathlihen old cemetery and she was struck by the almost inaccessible wilderness of the site. Assisted by her family she began a cleaning-up project shortly afterwards and continued the process over the next two and a half years until the site was well-defined by paths and lawns and all of the old headstones were re-positioned. Rev. Michael Moorhead, C.C., kept in touch with progress.
On 10 June 1985, Mrs. Daly began clearing this area, taking care not to dig too deeply at the inner end of the vestry. As she prised up an old tree stump with her pick-axe, she noticed pieces of an old mortar slab. Beneath this slab she was stunned to find the headless skeletal remains of a body obviously that of the late Fr. Molloy. The grave was carefully closed and a slab of concrete was subsequently placed over it. Some time later Fr. Moorhead composed the following tribute to Fr. Molloy: 'To the glorious memory of Fr. Edward Molloy who, during Penal times, was condemned to be hanged and beheaded because he was a priest. His headless body was eventually buried here. God be praised in his martyrs'. These lines were inscribed on a stone plaque which now stands at the spot, attracting visitors to pray for his soul.
History records that around 1691, the Parson of Lynally reported Fr. Molloy to the Protestant bishop of Meath stating that he had taken over the Church at Ballyboy and was saying mass constantly therein. One night while visiting Biddulph's house (Rathrobin), a man named Horan from Clonaslee arrived informing the priest that he was urgently needed for a sick-call. Biddulph advised Fr. Molloy against going, but the priest felt it was his duty to go. There was no sick person, but a house surrounded by soldiers. They arrested Fr. Molloy and took him to Brittas where he was hanged at the order of Col. Dunne. His body was decapitated, his head being displayed on a spike at the gate of Brittas, his body being buried under the hanging tree. Some nights later, during a thunder storm, some men from Killoughy travelled to Brittas, dug up his body and buried it without the head in the vestry of Rathlion church.
Today, Rathlion has become a place of pilgrimage, its serene surrounds and striking history making a deep impression on the visitors from Britain, the European Continent and further afield.