The monument includes the remains of a motte and bailey and shell keep castle and parts of a medieval chapel and graveyard, situated in a prominent position on the summit of a hillock above the River Wansbeck to the north and the Park Burn on all other sides; part of a medieval field system is situated at the northern foot of the hillock. The shell keep castle, the stone walls of the outer ward and associated structures, the remains of the chapel and two medieval headstones are Listed Buildings Grade I. An adjacent World War II pill box is the subject of a separate scheduling. Mitford Castle was first mentioned in 1138 when it was referred to as the `oppidum' of William Bertram, and it is known to have been occupied by William the Lion in 1175. It was confiscated by King John in 1215 and attacked unsuccessfully by the Scots in 1217. In 1317 the castle became the headquarters of Sir Gilbert Middleton but was captured and occupied by the Scots in 1318. By 1323 the castle was reported as being so damaged that it had to be abandoned. In 1327 it was described as being `wholly burnt'. The motte, later occupied by a shell keep, is visible as a substantial earthen mound measuring 56m north east to south west by 34m, situated at the centre of the north west edge of the knoll. There are traces of a surrounding ditch visible on its northern side. An oval bailey, situated to the south and south east of the motte, occupies the entire summit of the hill and measures 150m north east to south west by 75m north west to south east. The southern half of this bailey was later enclosed by a curtain wall to create an outer ward associated with the shell keep; the northern half of the bailey was retained as an undefended barmkin with an earthen bank between 1m to 2m wide and standing 0.4m high around its edge. On the lower ground to the north and south, the bailey is defended by a series of outworks; on the south west sides these include a ditch 10m wide and up to 2m deep with a flanking counterscarp bank. A similar ditch exists on the south eastern side where it has been disturbed by later quarrying which has also removed a section from the southern part of the bailey. On the north western side, the outworks include a triangular shaped platform and an outer moat a maximum of 1m deep. A `D'-shaped shell keep was constructed around the perimeter of the motte during the 12th century, creating an inner ward. The west wall and part of the east wall of the shell keep, which are constructed of high quality squared stone, are visible, each containing the remains of an arched entrance. Within the interior of the shell keep there are the remains of a central tower of early 13th century date. The tower is visible as the lower courses of a five sided stone building which measures 11m square with walls 2m thick. The basement of the tower is divided by a wall into two chambers, each with a barrel vault. These chambers are thought to have been used as cisterns for water storage. The first floor of the tower has an entrance lobby at its south corner reached by an external stair. Immediately to the west of the central tower there are the foundations of a second building 30m square with splayed window loops; this is interpreted as an earlier tower subsequently replaced by the 13th century tower. An outer ward attached to the south side of the shell keep is visible as lengths of a curtain wall enclosing the southern half of the earlier earthen bailey. The wall, constructed of squared stone, is 7m wide and on average stands to over 20 courses high. A small postern is visible in its western side and to the south of this the foundations of a range of buildings are clearly visible. On the eastern side, the remains of at least three mural chambers and a garderobe are visible. On the north side there are the remains of a gateway giving access to the barmkin to the north. Part of the southern end of the outer ward was removed by a quarry before 1810; immediately on the edge of this quarry, there is a fragment of a small chapel of late 12th century date and an earlier graveyard. The chapel, constructed of squared stone, is visible as the lower courses of the east end of the north wall and the remains of a chancel arch. Immediately to the north and east and also underlying the chapel, there is an associated graveyard; partial excavation of this area in 1938 exposed several 12th century gravestones. Many of these stones have been subsequently destroyed but there is at least one headstone visible at the monument; a further headstone reported as having an incised cross on its surface cannot now be identified. The body slab of the latter was removed and is visible in the churchyard of the present parish church. Two recently uncovered body slabs are visible to the east of the chapel. Part of a medieval furlong or field is visible immediately north west of the outer moat of the motte and bailey on the north west side. The field is visible as the slight remains of ridge and furrow cultivation orientated north east to south west; the ridges are 5m wide and stand to a maximum height of 0.2m. All fence lines which cross the monument and the notice post situated on top of the motte are excluded from the scheduling, although the ground beneath these features is included.