Sweffling is in East Suffolk, between Saxmundham and Framlingham. The village is on a hill overlooking the river Alde, in rolling arable land. The church is in the centre of the village, set well back from the high street. St Mary's has a nave with a S porch and a N vestry at the W end, a chancel and a W tower. The nave has large, 12thc. quoins at the angles, and N and S doorways ofc.1200; the N now in the vestry and the S under a 15thc. gabled, knapped flint porch with a battlement, niches for sculpture and flushwork decoration. The nave itself is of flint and septaria, but the walls have been heightened with brick. The nave windows date from the 15thc. The N vestry is modern and mortar rendered. The flint chancel walls have not been raised like those of the nave, and the pitch of the roof is much steeper. In the E wall is an intersecting tracery window ofc.1300, and this wall contains the blocked heads and jambs of two small 12thc. windows; one near the apex of the gable and the other to the N of thec.1300 window. Neither is likely to be in its original setting. On the N and S walls are pointed lancets, and the segmental-headed S chancel doorway may be 14thc. Inside, the piscina, with cusping in the arch, is of the same date, but the chancel arch is low, broad and segmental, probably dating from the 18thc. Pevsner describes the tower as Dec. but it may be earlier as its diagonal buttresses are an addition, as is the upper storey of c.1300. The W window dates from the same time, and a flushwork panel has been added below it, with more flushwork on the buttresses. The parapet, unusually, is not embattled but has flushwork decoration. Repairs to the church were carried out by C. P. Cleverly of Stowmarket in 1978-82. Only the two nave doorways are recorded below.

Domesday records large holdings in Sweffling that had belonged to William Malet (d.1071), and were held by Count Alan in 1087. Of these, Osmund held 30 acres as a manor before the Conquest, with two acres of meadow; five free men held 54 acres and four acres of meadow before the Conquest; and fourteen free men held 94 acres of ploughland and six acres of meadow. William Malet's son Robert also held land that had belonged to his father. A manor of 60 acres that belonged to Osbern before the Conquest was held by Robert de Claville from Robert Malet in 1086. Five acres that belonged to Beorhtnoth before the Conquest were held by Robert fitzFulcred from Malet in 1086. A manor of 60 acres held by Aethelwig before the Conquest was also held by Robert fitzFulcred from Malet. Ninety acres held by eleven free men before the Conquest also include four acres of meadow and a church, and were held by Robert fitzFulcred from Malet in 1086. A final holding was in the possession of one Ralph, who held it from Roger Bigod. This consisted of a manor of 60 acres held by Wulfric before the Conquest, together with nine acres and two acres of meadow added to it. Some property in Sweffling had passed to the Priory of Austin Canons at Little Leighs (Essex) by 1291, and at the Dissolution of Little Leighs in 1536, the manor of Denford in Sweffling passed to Richard Cavendish.

Upper Alde benefice, i.e. Badingham, Bruisyard, Cransford, Dennington, Rendham and Sweffling.

Pevsner calls the doorways Transitional, Cautley prefers late-12thc. for the S doorway, but it comes to the same thing. St Ethelred's, Tannington seven miles NW has an almost identical example.