Llanfechell means Church of St Mechell - the M softening to F in the Welsh genitive, pronounced V. Mechell, or Mechyll, was a sixth-century missionary, possibly from Brittany, said to have been the son of Echwydd and grandson of Gwyn Gohoyw, both fifth-century. A seventeenth-century manuscript, Llanstephan MS. 125, preserves a Welsh poem called Cywydd i Fechell Sant - a hymn to Saint Mechell. The poem tells how a man healed by the saint offered him a gift of land, with the boundaries to be marked by the path of a released hare. The hare ran, under divine guidance, along what is now the perimeter of the parish of Llanfechell, and there Mechell founded his monastery. The first written reference to the village dates to 1291, but the prehistoric remains scattered through the parish - standing stones, burial mounds, enclosures - confirm that people had been living here for thousands of years before the saint or the hare arrived.

On the edge of the village stands Brynddu, an estate held by the Bulkeley family and their descendants for five hundred years. William Bulkeley (1691-1760) was born here, kept a meticulous daily diary from 1734 until his death, and provides historians with one of the most detailed surviving records of eighteenth-century Anglesey life. He recorded the weather, the markets, the harvest, the gossip, the prices of cattle at Llanfechell fair. His daughter married Fortunatus Wright, a Liverpool brewer who became a notorious privateer in the Mediterranean - cutting Greek-flagged French ships from under their owners' noses with private letters of marque from the British crown. Today Brynddu is a 900-acre farming estate run by Robin Grove-White, the former director of the Campaign to Protect Rural England and chair of Greenpeace UK. A war memorial stands in the village square recording the dead of both world wars, including three sons of Brigadier-General Owen Thomas of Brynddu, the man who commanded Lloyd George's Welsh Army.

Three large stones stand together a short walk from the village, their long axes aligned north-west to south-east, each about 6.6 feet tall. The Llanfechell Triangle dates to the Bronze Age - a deliberate arrangement whose meaning the people who placed it took with them. Half a mile north on Pen-y-Morwydd hill, a burial mound 27 yards across and 6.6 feet high rises through the modern field wall that bisects it; nearby on the same hill, the Llifad enclosure - pentagonal, 49 yards across - was likely a later defended settlement. To the east, near Cromlech Farm, may be the remains of a burial chamber, though archaeologists hedge that it could simply be a 'suggestive natural feature.' A more recent local mystery surrounds the engraved standing stone discovered at the school: rock engravings are very rare in north Wales, and its significance remains unknown. The original is now in Oriel Ynys Mon Museum at Llangefni.

St Mechell's Church (Grade II* listed) has features dating back to the twelfth century, with whitewashed stone walls, a single-bell tower and an unusual cupola crowning the whole. Saint Mechell's Day is 15 November; the church holds bilingual services in Welsh and English every Sunday at ten. Ebenezer Chapel, on Mountain Road, was built by Welsh Independents in 1862 to replace a chapel from soon after 1800. Both are listed. Between the church and the chapel sit four watermills and three windmills, all in ruins or converted. Meddanen Water Mill and Melin Mechell Windmill stand close enough together that they may have been worked by the same miller, swapping power source by the weather - water when the streams ran, wind when the air did. Melin Mechell fell out of use in the early twentieth century and was converted into a house in the late 1970s. The village still holds an annual fair in late July - no longer for livestock, as in Bulkeley's day, but for horticulture and family games, on the grounds of Llanfechell Community School.