St Mary's consists of a square-ended chancel with N vestry and N organ transept, a clerestoried nave with north and south aisles and a S porch, and a west tower, all of brown cobble with a good deal of squared ironstone in the tower. In 1930 the church was seriously damaged by fire, and it was practically rebuilt by Sir Albert Richardson following the original design and reconsecrated in 1932. Originally, the tower (largely undamaged by the fire) dated from the 14thc., and the remainder largely from the 15thc., but with the re-use of 14thc. material in the form of the arches of the S nave arcade and the S nave doorway. The original organ transept was a 19thc. addition. A brick parish room has recently been added on the N side, communicating with the church through the N nave doorway. The Purbeck font is the only 12thc. feature.

Eaton Socon was transferred to Huntingdonshire from Bedfordshire in 1965, and it is under the latter county that it appears in Domesday. Before the Conquest the manor was held by Wulfmar of Eaton, a thane of King Edward, but William I gave it to Eudo FitzHubert. At his death in 1120 it reverted to the crown, and was subsequently given to the Beauchamps. In 1156 Hugh de Beauchamp bought the manor from his father. The Domesday record mentions no church, but the manor was one of only 55 in the country with a vineyard.

Pevsner (1968) noted the presence of architectural fragments. These have been investigated and what could be found relate to a 13thc. doorway with shaft rings, so are not included here. St Ives has an octagonal font with similar intersecting arcading, but not of Purbeck.