Dereham (/ˈdɪərəm/), also known as East Dereham, is a town and civil parish in the Breckland District of the English county of Norfolk. It is situated on the A47 road, about 15 miles (25 km) west of the city of Norwich and 25 miles (40 km) east of King's Lynn.
The civil parish has an area of 21.51 km2 (8.31 sq mi) and, in the 2001 census, had a population of 15,659 in 6,941 households; the population at the 2011 census increased to 18,609. Dereham falls within, and is the centre of administration for, Breckland District Council. The town should not be confused with the Norfolk village of West Dereham, which lies about 25 miles (40 km) away.
Since 1983, Dereham has been twinned with the town of Rüthen in North Rhine-Westphalia, Germany. It is also twinned with Caudebec-lès-Elbeuf, France. In spite of the reunification of Germany in 1990, the sign on the A47 at the entrance to Dereham from the Swaffham direction still refers to Rüthen being in West Germany; this sparks periodic comment in the local press.