The Thornhams, Magna and Parva, flank Thornham Hall and its park. Until the end of the 19thc. the estate boasted a hall, Tudor with an 18thc. facade, surrounded by an extensive park. Most of the hall was demolishedc.1900, and the rest was destroyed by fire in the late 1940s. The present hall is modern, and the estate has been converted for use as a field centre, a commercial market garden and a site for small businesses. Excavations in the estate have provided evidence of continuous occupation in the area from the Neolithic period to the present. The surrounding landscape is flattish and given over to arable cultivation. Thornham Parva lies to the N of the hall, some 2 miles W of Eye in central North Suffolk. The settlement is dispersed and sparsely populated with no real centre apart from the church, which lies just off the road from Thornham Magna and the Hall.

St Mary's has a nave and chancel in one, covered with a thatched roof, and a low W tower with a thatched pyramid roof. The church is of flint with ashlar dressings. The nave is apparently 12thc., with N and S doorways and a S window surviving from that period, but a round window visible in the interior W wall of the nave is said to be late Anglo-Saxon by Cautley. A flowing tracery window has been added on the S wall, and 15thc. windows have been inserted towards the W end. There is no chancel arch, and two Y-tracery windows on the lateral walls towards the E suggest a date ofc.1300 for the chancel. The E window is three-light reticulated, and there is a 15thc. S window. The tower is of knapped flint with no buttresses; it has a tall plinth course and a 15thc. main W window. Its E quoins are of brick, as are the upper windows, except for their ashlar ogee heads, suggesting an 18thc. date for the top of the tower. St Mary's is celebrated as the home of a 14thc. retable, probably painted for the Dominican house at Thetford. It was discovered in a stable loft at Thornham Hall in 1927 and given to the church by Lord Henniker. Romanesque work recorded here is found on the two nave doorways and the S nave window.

Thornham Parva was held by Robert Malet in 1086. There were various small parcels here before the Conquest: 7 acres held by two free men commended to Eadric (these were held by Robert’s mother in 1086); 28 acres held by 8 free men commended to Wulfgifu; 15 acres held by two free men, one commended to Wulfgifu; and 14 acres held by Sigeric, also commended to Wulfgifu (these three holdings in the hands of Robert Malet in 1086). There was three parts of a church in 1086 with 10 acres of free land. The present lords of Thornham are the Hennikers; it has been in the family since the mid-18thc.

South Hartismere benefice, i.e. Gislingham, Mellis, Stoke Ash, Thorndon with Rishangles, Thornham Magna, Thornham Parva, Thwaite and Wetheringsett cum Brockford.

Arch profiles with angle rolls and quadrant face hollows are locally common, as in the N doorway of St Mary's, Horham and both doorways at St Mary's, Pakenham.