1868–1885

• The Hundreds of Walsham, Blofield, Henstead, Humbleyard, Loddon, Clavering, Diss, Deepwade, Earsham, Guiltcross, Shropham, Taverham, Forhoe, and Mitford.^[4][5]

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.^[6]

The northernmost 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.^[7]

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 (later renamed the Loddon 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.^[7]

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 (combined) Rural District of Forehoe and Henstead was transferred to the new constituency of Central Norfolk, but Wymondham (which had been created as a separate Urban District in 1935) was retained.

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.^[7]

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.^[8]

Thetford and the area comprising the former Rural District of Wayland, including Attleborough, which had been included in 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.^[9]

The two excluded wards 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.^[10]

Cringleford and Colney (but not New Costessey) were transferred back from Norwich South. Seven District of South Norfolk wards, including Wymondham and surrounding areas, were transferred to Mid Norfolk.

Proposed

Further to the 2023 Periodic Review of Westminster constituencies, enacted by the Parliamentary Constituencies Order 2023, from the next general election, due by January 2025, the constituency will be composed of the following wards of the District of South Norfolk (as they existed on 1^st December 2020):

Brooke; Central Wymondham; Cringleford; Easton; Forncett; Hempnall; Hethersett; Loddon & Chedgrave; Mulbarton & Stoke Holy Cross; Newton Flotman; North Wymondham; Old Costessey; Poringland, Framinghams & Trowse; Rockland; South Wymondham; Stratton; Thurlton.^[11]

The seat will undergo major changes, with areas to the north of the River Waveney, which forms the boundary between Norfolk and Suffolk - including the towns of Diss and Harleston - forming part of the newly created, cross-county boundary, constituency of Waveney Valley. As part compensation, the town of Wymondham will be regained from Mid Norfolk. Other minor changes due to ward boundary revisions.

MPs 1868 – 1885 (two seats)

MPs since 1885 (one seat)

Notes:-

• ^a Cozens-Hardy stood at the 1918 United Kingdom general election as a Liberal without the Coalition "coupon", but he took the Coalition Liberal whip when Parliament assembled in 1919.
• ^b Baker was expelled from the House of Commons in 1954 after being convicted of fraud, forgery and uttering and sentenced to seven years imprisonment.

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• Caused by Howes' death.

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