St Mary’s stands at the Sern end of a strip of woodland that was once much larger. It is not served by any road, and must be reached by a walk of a good half-mile, skirting arable land and passing through the wood. The nearest building is Depden Hall (now a bed and breakfast), which is some 400 yards away and includes fabric reputed to date from the 14thc. The village itself has fragmented into settlements at Depden Green to the N and along the A143 to the E of church and hall. St Mary’s is a light and airy flint-faced church of nave, chancel and W tower. The aisleless nave has a 12thc. S doorway protected by a modern flint and brick porch that has been fitted with a skylight and a tiled floor, and converted for use as a kitchen and storeroom. The N doorway is later, and has a modern concrete and timber porch. The nave walls have Y-tracery windows ofc.1300, mostly restoration but with some original tracery. The S wall appears to have been refaced recently. The chancel has a late-13thc. piscina, and windows of a similar stylistic date (although they are largely 19thc. work). At the E end, diagonal buttresses with flushwork and capped by little stumpy pinnacles have been added. The tower and its arch can be dated to the mid-15thc. by a bequest of 1451. The tower has diagonal buttresses, flushwork on the plinth, a stair turret at the SE angle, and an embattled parapet. The chancel and nave were described as 'already restored' in 1837 (Church Plans Online). A fire in the 1980s gutted the nave, and the roof was replaced with the present arch-braced construction. The architects were Whitworth and Hall of Bury St Edmunds.

Before the conquest, Depden was held by Thegn Toki as a manor, and in 1086 it had passed to Hugh de Wanchy (Wancey), who held it from William de Warenne. This manor had three carucates of arable land, 12 acres of meadow and enough woodland for 100 pigs. There were actually 72 pigs in 1086, and 17 cattle, 112 sheep and 13 beehives, as well as a church with 24 acres of land. Two more holdings in Depden, each of two carucates, were held by Frodo, the abbot’s brother, and by Osbern in 1086. The manor remained in the de Wanchy family until the lordship of Sir Edmund de Wanchy, but at his death in 1372 it had evidently passed to Sir Nicholas Damery. In 1428 it was held by Alice Wildesher, a de Wanchy before her marriage, and by 1443 it had passed, presumably by marriage, to Thomas Gournay. The Gournay (Gurney) family were still at the manor in 1547, but at Anthony Gurney’s death in 1555 it passed to John Jermyn, whose mother, Lady Anne Drury, has a memorial in the church. She had married Sir Thomas Jermyn, her second marriage. Thomas died in 1552, and his will makes it clear that he considered himself Lord of Depden, even though Anthony Gurney was in possession of the manor.

The rather plain S doorway has similarities to that at Wixoe, in the angle-tucked cushion capitals and the form of the chevron roll, set back from the angle of the order without any elaborate edge treatment.