Onehouse is 10 miles E of Bury St Edmunds, just outside Stowmarket. St John's stands in arable farmland, with the moated hall site 100 yards to the south. It has an unaisled nave, chancel and round W tower. The tower, which bulges alarmingly in the middle, is of flint with a plain 13thc. lancet facing W and 13thc. bell-openings. Its embattled parapet is a later addition. The nave is of flint too, the south wall mortar rendered. On the N the render has been removed, and the masonry shows that it was originally shorter and lower. The original, shorter church may have been 12thc. Both nave doorways are plain 13thc. work, and the south has a 16thc. brick porch. The south nave windows have cusped Y-tracery,c.1300, but the cusping is inaccurately done. Buttresses of flint and modern brick have been added to each corner of the nave. The chancel was rebuilt by Herbert Green of Norwich in 1893. It is of mixed flint and rubble with brick quoins and gable; lateral windows in the samec.1300 style as the nave windows; and a three-light E window in the Perpendicular style. Some of the plaster rendering has been stripped off the interior walls, revealing them to be of flint in the nave but brick and flint in the chancel. There is no chancel arch. The only Romanesque sculpture here is the 12thc. font.

The manor of Onehouse was held by Ketil, a thegn of King Edward, before the Conquest, and by Ranulf Peverel in 1086. Ranulf's holding consisted of 1½ carucates of ploughland plus 20 acres, 12 acres of meadow and a church with 3 acres of free land. Other landholders in Onehouse in 1086 were Robert, Count of Mortain, who held 1 carucate that Wihtmaer had before the Conquest; a free man of St Edmundsbury abbey, who held a half carucate from the abbey, Osbern Masculus who held 26 acres as belonging to the church of Stow and Humphrey fitzAubrey who held 60 acres.

Benefice of Great Finborough, Harleston, Buxhall, Shelland and Onehouse.

Mortlock suggests that the tower is 'likely to be Saxon rather than Norman', but gives no reason for his opinion. He dates the font to the 12thc., and it is difficult to be more precise in view of the uniqueness of the design and the paucity of ornament on it.