1868–1885: The Hundreds of Walsham, Blofield, Henstead, Humbleyard, Loddon, Clavering, Diss, Deepwade, Earsham, Guiltcross, Shropham, Taverham, Forhoe, and Mitford. The seat was formed largely from southern parts of the abolished Eastern Division, with a small part transferred from the Western Division. 1885–1918: The Sessional Divisions of Depwade, Diss, Earsham, Loddon and Clavering, and Swainsthorpe. Northern-most parts were transferred to the re-established Eastern Division and western parts to the new Mid Division. It bordered Mid Norfolk to the west, the borough constituency of Norwich and East Norfolk to the north, the borough of Great Yarmouth and the Suffolk constituency of Lowestoft to the east and another Suffolk division, Eye, to the south. 1918–1950: The Urban District of Diss, the Rural Districts of Depwade, Forehoe, Henstead, and Wayland, and part of the Rural District of Thetford. Gained southern areas of the abolished Mid Division and a small area in the east of the South-Western Division. Lost eastern areas, which comprised the Loddon and Clavering Rural District, to the Eastern Division. 1950–1974: The Municipal Borough of Thetford, the Urban Districts of Diss and Wymondham, and the Rural Districts of Depwade, Loddon, and Wayland. These areas combined to produce a somewhat more urban constituency than before. Thetford was transferred from South West Norfolk and the Rural District of Loddon regained from the abolished Eastern Division. The Rural District of Forehoe and Henstead was transferred to the new County Constituency of Central Norfolk. 1974–1983: The Municipal Borough of Thetford, the Urban Districts of Diss and Wymondham, and the Rural Districts of Depwade, Forehoe and Henstead, Loddon, and Wayland. Regained the Rural District of Forhoe and Henstead, including Costessey, from Central Norfolk, which was now abolished. This was the last redistribution before a major reorganisation of local government, which amalgamated many of the smaller local authorities and which was reflected in the 1983 redistribution. 1983–1997: District of South Norfolk. Thetford and the area comprising the former Rural District of Wayland, including Attleborough, which had been included the District of Breckland, were transferred to the redrawn South West Norfolk constituency. 1997–2010: District of South Norfolk, except the wards of Cringleford and Colney, and New Costessey, which were transferred to Norwich South. 2010–present: District of South Norfolk wards of Beck Vale, Bressingham and Burston, Brooke, Bunwell, Chedgrave and Thurton, Cringleford, Dickleburgh, Diss, Ditchingham and Broome, Earsham, Easton, Forncett, Gillingham, Harleston, Hempnall, Hethersett, Loddon, Mulbarton, Newton Flotman, Old Costessey, Poringland with the Framinghams, Rockland, Roydon, Scole, Stoke Holy Cross, Stratton, Tasburgh, and Thurlton. Cringleford and Colney transferred back from Norwich South. Seven District of South Norfolk wards, including Wymondham and surrounding areas, transferred to Mid Norfolk.
