In 1086 a manuscript record of the Great Survey of much of England and Wales was completed in Medieval Latin by order of King William the Conquerer.
The fact that the Domesday Book (see top picture) records the existence of a church at Forncett St Mary suggests that it was already well-established, It may well be that Christian worship has been offered on this spot for 1000 years, or more. The coursed (or layered) masonry in the lower parts of the nave walls could well date from this period, and the tiny lancet window (see bottom picture) originally in the south chancel wall (now re-set in the north wall) shows work of c.1200 or slightly earlier.
During the 1400s St Mary?s, like most East Anglian churches, was given a thorough make-over during this period. The western tower was constructed when John Newman, parochial Chaplain at Tharston, made a generous bequest in 1432 towards the cost.
The windows were made in the latest architectural fashion the Perpendicular Style. The nave and chancel were given new north and south windows in this style, which admitted plenty of light and gave scope for the artists in stained glass. New north and south doorways were made, and a north porch added.