Trefin (probably derived from Tref (farmstead) and Ddyn (high ground) lies amid an area rich in early archaeology, including the remains of the Neolithic Chambered tomb at Carreg Samson, so called due to the legend of St Samson having placed the cap stone in position with his little finger.
The present church, the 5th to occupy the site, dates from 1869. It was designed by RK Penson. The light and spacious refurbished church has a new barrel vaulted ceiling and a new oak-finished floor.
In the west wall of the churchyard there are two inscribed stones from the 9th century, both bearing a simple cross in a circle. One was found in the wall of the farmhouse at Rhoslanog and in all probability this came from an earlier burial ground which is known to have existed in a field at a short distance to the south of this house. The second was removed from Tregidreg farm where is was used as a gatepost.
A stone in the church porch belongs to an earlier period, probably 5th or 6th century. The inscription is cut in Ogham script and reads: ‘Mac Cudicel son of Caticuus lies here’
The 12th century Book of Llandaff describes how St Teilo, walking beside the river Taf at Llanddowror rescued seven baby boys, whose father was too poor to provide for them. The saint baptised them and every day they received fish to eat from the river. Eventually they were sent to Mathry where for the rest of their lives they were known as the seven saints. In the 17th and 18th centuries a number of cist burials were discovered near the churchyard and these were instantly called the coffins of the martyrs.