Poslingford is in the SW corner of Suffolk, 2 miles N of the Essex border and 6 miles E of Haverhill. The village lies in the valley of a stream that runs S into the Stour at Clare, and a road following the same course forms the High Street. The church is in the village centre alongside this road, on the rising ground on the W side, and Poslingford Hall is immediately to the S of it.

St Mary’s has a nave with a S porch, a chancel and a W tower. The nave is of flint with 12thc. lateral doorways. The S doorway, with a carved tympanum and richly decorated capitals, is under a 15thc. brick porch, while the plain N doorway is blocked and has lost its arch. There is a plain 12thc. lancet on the N nave wall, but the other nave windows are late-13thc., 14thc. and 15thc. and are much restored, as is the flint walling. The chancel has late 13thc. lateral windows towards the W and Y-tracery and 15thc. windows further E. The plain piscina is 13thc. The E wall is entirely rebuilt, with a 19thc. triplet in the Early English style, and the lateral walling is refaced. The tower arch is a late 13thc. doorway with three chamfered orders. The flint tower itself has late-13thc. windows in its lower storey, diagonal W buttresses, and a top storey with 15thc. bell-openings and a battlemented parapet. An application to the Incorporated Church Building Society for a grant for reseating and general repairs by A.A.G. Colpoys of Sussex in 1881-82 was rejected, but the church has certainly undergone considerable 19thc. restoration. Romanesque sculpture is found on the S doorway and the font.

The largest landholder in Poslingford in 1086 was Ralph Baynard, whose holdings consisted first of a carucate of land and 20 acres with woodland for 5 pigs. A further carucate and a half was held by Norigaud from Ralph, and another carucate and a half with four acres of meadow by Walter from Ralph. Richer also held, from Ralph, 160 acres and a church with 40 acres of land attached. An estate here is recorded under the holdings of St Edmundsbury Abbey in 1086. Before the Conquest it was held by 12 free men of the abbey, and it consisted of 60 acres of ploughland. Another estate of 35 acres with two acres of meadow was held by Richard fitzGilbert in 1086, and by Eadric, a free man, before the Conquest. The Baynard family founded the priory of Austin Canons at Little Dunmow, Essex, in the early 12thc., and in the 1291 taxation Poslingford church was one of its properties. It remained so until the Dissolution.

Stour Valley Group, i.e. Clare, Poslingford, Cavendish, Stoke by Clare and Wixoe.

Motifs similar to those on the S doorway tympanum are found on the font at Preston St Mary, 11 miles to the E.