The house has a 12th-century private chapel built of flint and stone, with an early brick tower.

[2] For most of its history Stonor was called Upper Assendon and was a hamlet in an exclave of Pyrton parish.

In 1581 the Jesuit priests Edmund Campion and Robert Parsons lived and worked at Stonor Park, and on 4 August 1581 a raid on the house found a press on which Roman Catholic publications had secretly been printed.

[4] In the first half of the 19th century, the number of Roman Catholics in Upper Assendon increased, partly by local people converting, possibly aided by the fact that the only local school at the time was a Roman Catholic one endowed by the Stonors.

The 1851 census recorded 50 Catholics in the village, but in the final quarter of the 19th century the numbers sharply declined.