Merton is 3 miles S of Bicester in E Oxfordshire. Although there is documentary evidence that a church existed here before 1118, the present one is mainly of 14thc. build or later. Originally an impressive 14thc. church with some Perpendicular additions, its N aisle was demolished in the 15thc. or 16thc., leaving the piers and arches embedded in the N nave wall. Its spire was taken down in the 18thc. The only visible evidence of its origins now is a font that appears to be late 12thc. (Sherwood and Pevsner, 1974).

In 1086 Merton belonged to Countess Judith, niece of the Conqueror. It probably formed part of the earldom of Huntingdonshire and Northamptonshire, granted by the Confessor to Earl Walthoef, and assigned as dowry to Judith on her marriage to him. Thenceforth Merton followed the descent of the honor of Huntingdon.

Sometime between 1118 and 1136 the advowson of Merton church was granted to Eynsham Abbey by the antecessor of Guy de Cahaines. His successor refused to recognise the abbey's rights and attempted to exercise the patronage himself. He was ordered by Alexander, Bishop of Lincoln 1123-48, to restore the advowson to Eynsham. The abbey recovered it because shortly after, it secured its title against possible encroachments by the Templars. It obtained a mandate from Malcolm IV, King of Scotland, probably in 1145, ordering the Templars to allow the abbey to hold the advowson.

St Swithin’s belongs to the Ray benefice that consists of Ambrosden, Charlton-on-Otmoor, Islip, Merton, Noke, Oddington, Piddington and Wood Eaton.

There seems no good reason for doubting Sherwood and Pevsner's assessment of the font as being late 12thc.