The date that the castle was built is unclear. Between 1154 and 1175 it was in possession of the Earl of Cornwall and it had become a royal possession by 1185. Both Henry III and John spent money on the castle. It appears to have been disused from about 1290 and there are references to its stonework being reused by the Chidlock family to build Dorchester Greyfriars in 1309. Certainly it was abandoned by 1422.
Dorchester Prison occupies its site - originally to the north of the town, with an Franciscan Priory further east, but nothing of the castle or the priory remain. However, in 1720, two underground passages were discovered while building a chapel: these once connected the castle to the town proper. In the 1800s, a bastion-like rampart still existed, and a small rampart and ditch were visible on the north and east sides. The gatehouse was built in 1790 and has been designated as a Grade II listed building.
There are some records of people associated with the castle:
- 1216-17 - John Marshall, Earl of Pembroke was appointed governor 
- 1270 - William Belet was granted the castle along with a park
- Draper, Jo (1982-01-01). Dorchester Excavations: Excavations at Wadham House 1968, Dorchester Prison 1970, 1975, and 1978, and Glyde Path Road 1966. Dorset Natural History and Archaeological Society. p. 91. ISBN 9780900341106.
- "Dorchester Castle". Gatehouse Gazetteer. Retrieved 2016-08-02.
- Fry, Plantagenet (2005-10-15). Castles: England + Scotland + Ireland + Wales. David & Charles. ISBN 0715322125.
- Timbs, John (1872-01-01). Abbeys, castles and ancient balls of England and Wales, their legendary lore, and popular history. Re-ed. by A. Gunn. p. 440.
- Hutchins, John (1868). The History and Antiquities of the County of Dorset (3rd ed.). pp. 362–4.
- Schofield, John; Leech, Roger, eds. (1987). "Urban Archaeology in Britain". Archaeology Data Service. ISBN 0906780594. Retrieved 2016-08-03.
- "British History Online". www.british-history.ac.uk. Her Majesty's Stationery Office. 1970. Retrieved 2016-08-03.
- Mackenzie, James Dixon (1896). The castles of England, their story and structure. p. 246. ISBN 9781153325301.
- "The stone gateway forming the north elevation of the gatehouse of the former Her Majesty's Prison Dorchester". National heritage List for England. Historic England. Retrieved 26 August 2016.
- Fry, Plantagenet Somerset, The David & Charles Book of Castles, David & Charles, 1980. ISBN 0-7153-7976-3.
- Dorchester Castle, at Pastscape
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