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. The civil parish, covering an area of 29.55 km2, in 2011 had a population of 24,340. 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.