St. Mary's Church in Llanfair Caereinion is on a site that appears early medieval, and it is claimed that a church has been in evidence there since the eleventh century at the latest. It first appears in the historical record in 1239.
Although St. Mary's was demolished and rebuilt by Edward Haycock in 1868, much of the original geometric plan was maintained, with a continuous nave and chancel incorporating the vestry, west tower, north aisle and south porch. In addition, a great deal of early material was incorporated into the rebuilt structure; the south porch can be dated to the early thirteenth century, and although the font has proven difficult to date, it appears to be from the same period. The timber roof structure is of the fifteenth century, with some original timber beams apparently carved. The stone effigy of a knight, Dafydd ap Gruffyd Vychan, dates to approximately 1400. To the northeast of the churchyard is St. Mary's Well, (NPRN 32455) which was believed to have been pre-Christian to have had curative powers.
The church is built primarily from grey quarried sandstone blocks, with pink and yellow sandstone dressings. Until 1884 the tower was a timber construction on a stonework base, but was replaced with a stone 3-stage tower by A.E. Lloyd Oswell in 1885.

Source: Cadw Listed Building Record
RCAHMW Inventory Documents

K Steele, RCAHMW, 17 November 2008