Whepstead stands on a low hill in the largely arable farmland of W Suffolk, some four miles S of the centre of Bury St Edmunds. The village is small, consisting of a few houses with outlying farms along the B1066 and its side roads; the church is on one of these minor roads W of the village centre. St Petronilla's has a nave, chancel and W tower. All windows of the nave and chancel are Y- or intersecting tracery ofc.1300, or other early 14thc. forms. The N and S nave doorways are 13thc.; the S under a knapped flint 19thc. porch, and the N now giving access from the church to a vestry. The nave is broad and bright, with a chancel arch having 12thc. jambs and a round head decorated with 19thc. neo-Romanesque chevron. There is a S rood stair set in the E reveal of the easternmost nave window. A scar on the E wall of the tower shows that the nave was originally taller. The 15thc. tower arch is tall and four-centred and a wooden gallery has been erected halfway up it. The tower is 15thc. too, and was repaired in 1582 (date on buttress). It has very broad E buttresses with a stair turret set in the angle of the SE buttress, diagonal W buttresses and an embattled parapet. It was apparently taller when built, and certainly had a spire but a storm in 1658 brought the spire down, and the battlements postdate that collapse. The church is entirely mortar rendered except for the S porch, the chancel E wall and the parapet of the tower, all of flint. The only Romanesque sculpture is found on the chancel arch.

The Domesday Survey records that St Edmundsbury Abbey held Whepstead as a manor with 5 carucates of ploughland, 10 acres of meadow and woodland for 40 pigs. In the same place were 6 free men with 11/2 carucates of land, held by Ralph except for 30 acres. There was a church with 30 acres of free land. The abbot's manor house at Whepstead was one of 13 burnt by disaffected townsmen and tenants during the so-called Great Riot of 1327; a protest against the abbey's bad management of their estates and their alleged failure to meet their commitments.

At the Dissolution the manor came into the possession of the Drury family, lords of Hawstead.

In 1535 part of the income of the leper hospital of St Petronilla in Bury St Edmunds was derived from temporalities in Whepstead, which may account for the unusual dedication.

Benefice of Horringer with Westley, Whepstead and Brockley.

An earlier dedication to St Thomas of Canterbury is known, but this is unlikely to have survived the Reformation. The dedication before St Thomas's canonisation in 1173 is not known. The chancel arch jambs appear earlier than this, probably before 1140, but their simple form and lack of bases precludes any more precise attempt at dating.