Gilston is a village in the East Hertfordshire district, less than half a mile from the Rover Stort, which forms the Essex border at this point. It is 7 miles E of Hertford, but the nearest town is Harlow, a mile to the S in Essex. The church is a mile outside the village to the NW. St Mary's has a nave and chancel in one with a N vestry to the chancel and narrow nave aisles with a timber S porch. The W tower doorway is 13thc, but above it the tower is of 16thc brick for most of its height, with a flint battlemented parapet and a slender lead-covered broach spire. The flint-faced nave (including the blocked N doorway) and chancel are 13thc, the knapped flint S aisle was added or rebuilt in the 19thc, along with the vestry and the S porch. The only Romanesque feature here is the Purbeck font.

Gilston is not mentioned by name in the Domesday Survey. Following the account in VCH, it was probably included in the manor of Sawbridgeworth, held by Geoffrey de Mandeville. By the end of the 12thc the Mandevilles had found tenants for the manor but retained the overlordship, which passed to the Says, and then the Bohuns, Earls of Hereford and Essex. There were two tenancies, corresponding to the manors of Overhall and Netherhall, and since the former contained the church this will be described here. It was held by the Ros family in the 13thc and it remained in that line until 1375.

The church was given by Geoffrey de Mandeville to the abbey of Walden, Essex, which he founded. At his death in 1144 the advowson was contested, and was eventually awarded to the Bishop of London, remaining with the see until 1852.

Overhall, where the church stands, is represented only by the farm of that name alongside the church. There are groups of cottages nearby, but the List Description is doubtless correct in laelling it the church of a deserted medieval village. As in most southern counties with a shortage of local building stone, fonts of paludina limestone (the so-called Purbeck and Sussex marble) were commonly imported into Hertforshire in the 12thc-13thc. The hexagonal form is unusual; generally the earlier ones are square and the later ones octagonal. A date at the end of the 12thc is suggested by RCHME, which dates the stem to the late 14thc.