The church has a short chancel with a low roofline. The bell-turret, N aisle and E windows are from 1885 (Pevsner 1967, 84). The Romanesque nave is long and thin; it has retained its chancel arch, doorway and three windows to the S.

The exterior is rendered with cement, painted cream; quoins and stones around windows and doors have been left clear of render.

In 1086 the manor was held by the king’s thegn, Ulfkil. No church is recorded, but Earnwine the priest had half a plough there (Williams 1992, I, fol. 330v).

William Earl Warenne gave the church of Little Sandal with the chapel of Armthorpe (Hernoldsthorpe) to Lewes Priory in the time of Henry I. Some part also belonged to Roche (Hunter 1823, 1:86-89). Hunter describes it as a "Small building of one pace [sic] with two bells hanging in a kind of pent-house of the roof." It is the only church in the deanery without a tower.

Pevsner says of the chancel arch ‘unmoulded, on the plainest imposts’; evidently missing the decoration on the southern impost.

Patterns laid out within a grid are common, but a prominent raised grid like this is rare; compare the tympanum and lintel of the W doorway at Long Marton (Cumberland). The presence of the raised grid suggests that what was required to be carved here was not known to the workman in its usual sculptural form. Compare the imposts of the chancel arch at Copgrove (West Yorkshire), these are both carved on upright and chamfer; the patterns used are again vertical chevrons and chip-carved saltire stars, also slanting incised zigzag. In more accomplished work, as in the majority of Norman architectural decoration, any patterns would normally be on the upright of the impost only, compare the doorway at Kirkby Malzeard, which uses star-in-square. It is the absence of the overseer, priest or client from the workshop at Armthorpe that may account for the fact that two patterns are carved on one stone while the opposite one is blank (Landall, n.d., 3).