The area of Ampthill Park (public park) has probably been parkland since the 15th century when Ampthill Castle was built on the crest of the Greensand Ridge.
Ampthill Castle was built in the early 15th century by Lord Fanhope as a “residence meet for his royal spouse” Elizabeth, sister of Henry IV. It passed to the crown in 1524 and Katherine of Aragon lived at the Castle in 1533 during her divorce from Henry VIII.
By the later part of the 16th century the buildings were already in a state of decay and had been completely demolished by 1649. In spite of its name Ampthill Castle was never a castle in a military sense although it may have had some of a castle’s external trappings. Its true character was that of a palace with the emphasis on the domestic and the activities of an aristocratic household with royal associations.
The first castle here is described by Leland as “standing on a hill, with four or five faire towres of stone in the inner ward, beside the basse courte.” This structure has altogether disappeared. It was built by Sir John Cornwall, created Baron Fanhope in 1432, out of the spoils of war which he had acquired in France. He was a distinguished soldier and leader in the days of Henry IV. and Henry V., who, at Agincourt, had held a post of honour in the van, in company with the Duke of York. The romance of his story is, that at a tournament at York, in 1401, this knight, by his prowess and bearing, captivated the heart of the Lady Elizabeth, sister to the King, and widow of the Duke of Exeter, and married her. After the Fanhopes, the manor and castle of Ampthill came, in 1524, into the hands of Reginald Gray, Earl of Kent, and soon afterwards passed into the possession of the Crown, in the reign of Henry VIII. Here resided the injured Queen Katharine of Arragon, when, in 1529, she quitted Windsor for ever; and she was dwelling here when the decision pronouncing her marriage null and void was given at Dunstable Priory, in the same county, in May 1533. The castle was afterwards used as a royal residence by Henry, after his marriage with his sixth wife, Katharine Parr, ten years later, and to Ampthill was brought the Princess Mary (afterwards Queen) for recovery from an illness.
After this reign the place appears to have been left to decay, for in the survey of 1649 it is said to be utterly demolished. The existing house of Ampthill was built in 1694 by the first Lord Ashburnham. Behind it are some fishponds, and above these, at the edge of a cliff, stood the front of the ancient castle. In the possession of Lord Holland are two ground plans of Ampthill, supposed to have been taken about 1616, at the time when the fabric was destroyed. They show that the area comprehended was a square of 230 feet, haying in front a large court, 115 feet by 120, and in rear two small ones, each 45 feet square, with an oblong courtyard between them. In front, the building had two square projecting towers, awhile around, at irregular distances, were nine other towers of different shapes, chiefly five-sided semi-octagons. (Castles Of England, Sir James D. Mackenzie, 1896)