The village stands on the southern bank of the Little Ouse that forms the boundary with Norfolk. The tiny village of Santon, which was subsumed into the parish in 1963, is over the river in Norfolk. Santon Downham is in the middle of Thetford forest and is now the home of the headquarters of the Forestry Commission for the East Anglian district. Downham Hall, N of the church, near the river, was the focus of a sporting estate until the early years of the 20thc., but the Mackenzie heir sold up in 1918, the Forestry Commission acquired the land in1924, and the hall was demolished from 1925. New houses for the Commission workers were built around the green, to the W of the church, in the 1950s, effectively shifting the village centre to the SW. Between 1920 and 1970 Santon Downham was almost entirely devoted to forestry, with almost all of its male inhabitants employed by the Commission. Since the '70s many of the residents have exercised their right to buy their houses, and less than one in twenty of the 250 present inhabitants work in forestry. The area was anciently dominated by warrens, with Santon Warren to the N, Santon Downham Warren to the S. These were set up in the Middle Ages (see Preface to Suffolk), often by the monastic houses of Ely and Bury. As at Lakenheath, the sandy soil was prey to sandstorms, especially if it was overgrazed by the rabbits, and one such engulfed the village of Santon Downham over a period of several decades, culminating in 1668.

St Mary's stands at the E end of the village green; which is little more than a clearing in the surrounding pine forests. It comprises an unaisled nave, chancel and W tower, all of flint with ashlar dressings. The nave has 12thc. N and S doorways, the N under a porch whose abnormally thick E wall may originally have been the W wall of the N chapel (see below). The western pair of side windows in the nave have round-headed arches and splays within but pointed lancets on the outside. There was once a chapel at the E end of the nave on the N side; its blocked 14thc. arch has been converted into a window, and its piscina remains, now on the exterior nave wall. The chancel has a S doorway ofc.1200, apparently re-set from the N wall. Otherwise the lateral chancel windows are 13thc. lancets except for one with flowing tracery on the S, indicating a 14thc. campaign. The E window is 19thc. and reticulated. The 14thc. campaign also included the chancel arch. The W tower, though plain and unbuttressed, is dated by wills to 1460-1503, so its 15thc. W window is an original feature. It has a polygonal SW stair. There was a major restoration in 1893. Romanesque features recorded here are the N and S nave doorways, the S chancel doorway, a relief panel set over the S nave doorway and a section of string course or possibly a lintel now re-set inside the chancel in the N wall.

The manor of Santon Downham was held by St Edmundsbury Abbey before the Conquest, and by Frodo, Abbot Baldwin's brother, in 1086. It had three carucates of ploughland, mostly held by nine free men owing customary dues to St Edmundsbury. Also recorded were meadow, a fishery and 21 pigs and 900 sheep. A church was recorded with 20 acres of land. Another holding in Santon Downham was in the hands of 'a half free man under soke to St Aethelthryth' (i.e. Ely). This included half a carucate and an acre of meadow. A John de Santon appears c.1170, and his granddaughter Alice married Robert de Vere, 5th Earl of Oxford (1240-96), which is the likeliest explanation for the manor passing to the de Vere family. The manor was subsequently subdivided, but a relevant feature of its history is the granting of Downham Ixworth manor to Ixworth priory in 1250-51. After the Dissolution it was granted to Richard Codington. The estate passed through many hands until it was sold to speculators in 1918. It was acquired by the Forestry Commission in 1924 and the hall was demolished in the following year.

Benefice of Brandon and Santon Downham with Elveden and Lakenheath.

The S nave doorway is more or less in its original state, although the abnormally narrow inner order with imposts treated as corbels is unusual. The trefoil capitals and arch profile suggest a date in the 1120s or '30s, and this is borne out by the bulbous forms of the base rolls. The N doorway is contemporary but its arch has been replaced with one that is stilted and chamfered, perhapsc.1200. This is the date of the S chancel doorway, which appears to have been moved from the corresponding position on the N, presumably to suit the convenience of the vicar. The decoration of the re-set string course section in the chancel matches that of the priest's doorway arch except for the cusping. Its form with unchamfered sections at either end suggested a lintel to Fitch, but his assertion that it 'would fit exactly as the lintel across the round arch' is not confirmed by the measurements. The most exciting piece, however, is the relief above the S doorway. Pevsner called it a lion, the identification accepted here. Fitch reported other opinions; the Paschal Lamb, or a wolf devouring the Tree of Life. That it is a lion seems verified by its pose and its mane, as well as the treatment of the tail; standard for lions in this period. The raised foreleg is uncommon, but the idea of a benediction is not so far-fetched given the lion's common identification with Christ (Baxter, 37-39). Fitch's comparison with capitals in the transept of Ely Cathedral is well-made. He also compares it with the S doorway tympanum at Wordwell, some 10 miles from Santon Downham, which is stylistically quite different but also includes lions and foliage. The panel could date fromc.1100, but may equally be contemporary with the nave doorways.