Astwell Castle is a manor house in Northamptonshire, England about 1.5 miles (2.4 km) south-west of Wappenham. It is a listed building and part of the parish of Helmdon, a village 1 mile (1.6 km) west.
The De Wauncys were amongst the earliest possessors of this manor since the Conquest. From them, it descended to the Brookes. On 24 April 1471, Thomas Lovett II acquired Astwell in exchange for his hereditary estates by a family arrangement with his mother's cousin, Dowse Billing and her husband William Brooke. The house was begun by Lovett.
George Shirley, Esq. (created a baronet, on the first institution of that order, by James I. in 1611), Lovett's grandson, was the next possessor. He partially or totally rebuilt the manor house. From him this manor descended to Washington Shirley, 5th Earl Ferrers by whom it was sold in 1763 to Richard Grenville-Temple, 2nd Earl Temple. He was succeeded by his nephew, George Nugent-Temple-Grenville, 1st Marquess of Buckingham, and whose son, Richard Temple-Nugent-Brydges-Chandos-Grenville, 1st Duke of Buckingham and Chandos was also associated with the manor house. Biddlesden Abbey had possessions in the manor. By 1874, the manor house had been largely dismantled, some of the "inferior offices" becoming a farmhouse, and a "broad embattled tower" remaining.
The embattled gatehouse tower with the lower attachment to the left is of Lovett's time. To the west, a large courtyard house with over forty rooms accumulated under later owners in the Lovett and Shirley families in the 16th and 17th centuries, of which only a fragment survives. It still has mullioned windows with arched lights, suggesting 16th rather than 17th century. Inside is a fireplace with a broad frieze of simple geometrical motifs above the four-centered arch. Early 18th century drawings show ranges added against both the west and south sides of the house which were built up to or over the moat. These may be related to infilling the moat and setting out a garden with formal terraces on the south and east sides of the house.