The two saints, Beuno and his disciple Aelhaiarn, came north from Powys in the seventh century under the patronage of King Cadfan of Gwynedd. Cadfan's son Cadwallon -- the same Cadwallon who would later kill the Northumbrian king Edwin at the Battle of Hatfield Chase in 633 -- reneged on a promised land grant to the monks. His cousin, embarrassed by the breach of hospitality, donated his own land instead, allowing Beuno and Aelhaiarn to found their monastery in this corner of the peninsula. The nearby river, the Afon Erch, contains a stone listed as Grade II* with a petrosomatoglyph traditionally said to be the marks of Beuno's kneeling -- worn through, the story goes, by his nightly visits to pray in the middle of the stream. During expansion of the churchyard at Llanaelhaearn in 1865, workers uncovered the Latin-inscribed gravestone of one Aliortus of Elmet, possibly indicating that there had been a religious settlement here before Beuno's monks arrived. Christianity was already old by then in this part of Wales.

St Aelhaiarn's Well -- Ffynnon Aelhaearn -- became one of the major stations on the northern pilgrimage route to Bardsey Island. Pilgrims would stop here on their way down the peninsula toward Aberdaron and the boats that took them across Bardsey Sound to the small island where the saints of Wales were said to be buried. The well's miraculous quality was its 'laughing' or 'troubling of the water' -- the irregular appearance of upwelling bubbles that broke the surface of the basin. Devotees believed the water laughed in the presence of those it would heal. By the nineteenth century the well was surrounded by an oblong stone basin with stone benches around it, where pilgrims would rest and wait for the water to bubble. Reports of cures continued well into Victorian times. Then, in 1900, a diphtheria outbreak struck the village and the council blamed the open well. The well was first enclosed and roofed, then locked away from the public altogether. The current enclosure dates from 1975. The water still bubbles, in private, behind a wall.

The hill that rises directly behind Llanaelhaearn is Tre'r Ceiri -- the town of the giants -- one of the most spectacular Iron Age hillforts in Britain. The summit, at 1,591 feet, carries the stone foundations of more than 150 round huts inside a substantial defensive wall. The wall in places still stands ten feet high, with original lintels over its gateways. Tre'r Ceiri was occupied from around 200 BC through the Roman period; the inhabitants traded with the Roman administration without abandoning their fortified hilltop. It is one of the best-preserved late prehistoric settlements in Wales, and on a clear day from the summit you can see across to Ireland. The peak forms the easternmost of Yr Eifl's three summits. Behind the village, then, sits a Bronze and Iron Age town. In front of it ran the medieval pilgrim road. The site has been important to people for at least two and a half thousand years.

In 2024, after consultation, the local community was officially renamed Trefor a Llanaelhaearn, recognising that the larger village of Trefor down on the coast had outgrown the parish that originally took the church's name. The change was unusual enough to attract press coverage in North Wales -- communities rarely change their names in Britain. The combined community population is 1,067, rising to 1,117 in 2011, with the electoral ward including the neighbouring community of Pistyll bringing the total to 1,683. Trefor itself grew up around the granite quarry that worked the eastern flank of Yr Eifl in the nineteenth and early twentieth centuries, producing the setts that paved Liverpool. Llanaelhaearn produced one Vice-Chancellor of London University -- Sir David Hughes Parry, who served from 1945 to 1948 -- and seventeen centuries of pilgrims walking past on their way to Bardsey. The village still keeps its church, its locked well, its hillfort overhead, and its quiet.