A large church comprising nave with N aisle, W tower, S transept and square-ended chancel. The church contains an important series of 12thc. corbels. Of these, a group of four are in their original positions on the S nave wall, below the level of the added clerestorey. One is reset at the SW corner of the nave. The remainder (18 in all) have been brought inside the church and reset under the roof trusses of the N, S and W nave walls, and on the N and S walls of the N aisle. Also present are a late 12thc. W doorway and tower arch.

Land in Cumnor was given to Abingdon abbey by King Caedwalla, but was taken back into royal hands after it was sacked by the Danes. In 955 King Eadred gave it back to Abbot Aethelwold, a grant confirmed by King Edgar in 968. The Domesday Survey mentions a church in Cumnor, which was then an important holding of Abingdon Abbey assessed at 30 hides, with two mills, fisheries and land for 50 ploughs.

The corbels of Cumnor are among the finest in the county, and are presumably the work of sculptors from Abingdon - they are certainly unlike the earlier Reading Abbey corbels. More or less comparable, though less impressive, examples survive at Aldermaston and Appleton Manor. The flat leaves of the W doorway capitals suggest a date of c.1160-80, as do the repetitive scallop capitals on the chancel arch.