Thetford is a market town and civil parish in the Breckland district of Norfolk, England. It is on the A11 road between Norwich and London, just east of Thetford Forest. There has been a settlement at Thetford since the iron age, and parts of the town predate the Norman Conquest; Thetford Castle was established shortly thereafter. The town was badly hit by the dissolution of the monasteries, including the castle’s destruction, but was rebuilt in 1574 when Elizabeth I established a town charter. Following World War II, Thetford became an ‘overspill town’ taking people from London, as a result of which its population increased substantially.The civil parish, covering an area of 29.55 km2 (11.41 sq mi), has a population of 24,340. Thetford railway station is served by the Breckland line and is one of the best surviving pieces of 19th century railway architecture in East Anglia.

Breckland was used as an excavation site for flint tools around 2000BC. During the iron age, a fort was established on Icknield Way at the site of Thetford Castle.Thetford was an important tribal centre for the Iceni during the late Iron Age and early Roman period, with Castle Hill and Gallows Hill being sites of particular note. During the Saxon period it was the principal centre of the eastern Heptarchy and a regular battle site between locals and the Viking invaders.[6] A mint was built in Thetford in the 9th century. A monastery was established around 1020 and a grammar school was operating before the Norman Conquest of 1066.The town greatly prospered during the reign of Edward the Confessor (1042–1066), and at one point there were 944 free Burgesses living in Thetford.The Domesday Book of 1086 estimated the population of Thetford to have grown to between 4000 and 4500 people, which would have been the sixth largest town in Britain at the time.The Book lists William of Bello Fargo as the Bishop of Thetford at the time. He had moved here from North Elmham in 1071 and stayed in Thetford until moving to Norwich in 1096.[3] Ruins of the Priory of St Mary In 1067-9, Thetford Castle was built on the ruins of an Iron Age fort at Castle Hill. It is believed to have been constructed either by Ralph Guader, Earl of East Anglia, or Roger Bigod, his successor as Earl, who is known to have ordered Bungay and Framlingham castles to have been built in Suffolk. In 1104, Bigod founded the Cluniac Priory of St Mary. The priory grew rapidly, with an influx of monks from Lewes, and in 1107 it was moved to a larger side on the other side of the river where the ruins remain today. It became the largest and most important religious institution in Thetford. The Norfolk Lent Assizes were held at Thetford from 1264 because there was only one Assize for both Norfolk and Suffolk.

Thetford, being close to the border between the two, was convenient for both. However, after much pressure, an Act of Parliament was passed in 1832 to transfer them to Norwich. In 1373, John of Gaunt, the Duke of Lancaster, was responsible for altering the administrative makeup of the town, promoting the Mayor to its most important official, subjecting the bailiff and the coroner to report to him. Thetford had its own coroner, courts and legal officials, without depending on those for the counties of Norfolk and Suffolk.