Although the subject of this watercolour has been identified as Dilston Castle since at least the time of its sale in 1855 this is not altogether certain. Dilston is about three miles south-east of Hexham, Northumberland. The name is derived from Devilstone and it lies on the Devil's Water shortly before it enters the Tyne. The ruins are those of the ancient castellated manor house of the Radcliffes, Earls of Derwentwater: the house was partly demolished after the execution in 1716 of James, 3rd and last Earl for high treason, when his estates were granted to the Trustees of the Greenwich Hospital.
Turner visited Northumberland twice in his early years, in 1797 (see D. Hill, Turner in the North, New Haven and London, 1996) and 1801 (ibid; pp. 56, 186).
However, the other special feature at Dilston besides the ruined manor house is the Lords Bridge over the Devil's Water and this is a large single-spanned bridge rather than the three-arched bridge shown in the watercolour. Other possibilities also have their disadvantages: Richmond Bridge and Castle, as portrayed by Turner circa 1798-9 (ill. in colour, Hill, op.cit, pl. 57), has a much more solid and four-square main tower, while at Warkworth, also visited by Turner in 1797, the old bridge, though of the same general type with butressed piers, is shown in old engravings as having only two arches. Perhaps Turner was indulging in artistic license.
To complicate things still further, there is a possibly related pencil sketch in the 'Dynevor Castle' sketchbook; this is mainly occupied by Welsh drawings of 1798 but, as David Hill points out, includes a small number of Northumberland subjects (A.J. Finberg, A Complete Inventory of the Drawings in the Turner Bequest, London, 1909, vol. I, p. 95, no. XL, p. 45; Hill, op.cit, p. 200, n. 23).