The Community Assembly of Thetford is located in a market town and civil parish in the Breckland District of Norfolk, 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 origin of the name Thetford is unclear. The site was an important crossing of the River Little Ouse, so one possibility is that the settlement drew its name from the Anglo-Saxon Theodford or people's ford. It is also unclear if the nearby River Thet is named after the crossing or the later settlement.

The town was badly hit by the Dissolution of the Monasteries, including the castle's destruction, but it was rebuilt in 1574 when Elizabeth I established a town charter. After World War II, Thetford became an 'overspill town', taking people from London, as a result of which its population increased substantially. 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.