1918–1950

• The Municipal Borough of Hemel Hempstead;
• The Urban Districts of Berkhamsted, Harpenden, and Tring;
• The Rural Districts of Berkhamsted and Hemel Hempstead;
• The Rural District of St Albans parishes of Harpenden Rural, Redbourn, and Wheathampstead; and
• The Rural District of Watford parishes of Abbots Langley and Sarratt.^[4]

1950–1974

• The Municipal Borough of Hemel Hempstead
• The Urban Districts of Berkhamsted, Harpenden, and Tring;
• The Rural Districts of Berkhamsted and Hemel Hempstead; and
• The Rural District of St Albans parishes of Harpenden Rural and Redbourn.^[5]

Wheathampstead was transferred back to St Albans. Abbots Langley and Sarratt now included in the new constituency of South West Hertfordshire.

1974–1983

• The Municipal Borough of Hemel Hempstead;
• The Urban Districts of Berkhamsted and Tring; and
• The Rural Districts of Berkhamsted and Hemel Hempstead.^[6]

Harpenden and the part of the parishes of Harpenden Rural and Redbourn were transferred back to St Albans.

The constituency was abolished for the 1983 general election. Berkhamsted and the area to the south of Hemel Hempstead, including Kings Langley, was transferred to South West Hertfordshire.  The remainder, including Hemel Hempstead and Tring, formed the new constituency of West Hertfordshire.

1997–2010

• The District of Dacorum wards of Adeyfield East, Adeyfield West, Ashridge, Bennetts End, Boxmoor, Central, Chaulden, Crabtree, Cupid Green, Flamstead and Markyate, Gadebridge, Grove Hill, Highfield, Kings Langley, Leverstock Green, Nash Mills, South, and Warners End.^[7]

Re-established for the 1997 general election from the bulk of the abolished County Constituency of West Hertfordshire (excluding Tring). Kings Langley transferred back from South West Hertfordshire.

2010–present

• The District of Dacorum wards of Adeyfield East, Adeyfield West, Apsley, Ashridge, Bennetts End, Boxmoor, Chaulden and Shrubhill, Corner Hall, Gadebridge, Grove Hill, Hemel Hempstead Central, Highfield and St Paul's, Kings Langley, Leverstock Green, Nash Mills, Warners End, Watling, and Woodhall.^[8]

Minor loss to South West Hertfordshire following revision of local authority wards.

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 Borough of Dacorum (as they existed on 1^st December 2020):

Adeyfield East; Adeyfield West; Apsley and Corner Hall; Bennetts End; Bovingdon, Flaunden and Chipperfield; Boxmoor; Chaulden and Warners End; Gadebridge; Grovehill; Hemel Hempstead Town; Highfield; Leverstock Green; Nash Mills; Woodhall Farm.^[9]

Moderate changes, with Kings Langley being transferred to South West Hertfordshire, in exchange for the rural Bovingdon, Flaunden and Chipperfield ward. The rural Ashridge and Watling wards to the north will be included in the newly created seat of Harpenden and Berkhamsted.

MPs, 1918–1983

MPs, 1997–present

Elections in the 2020s

Elections in the 2010s

This was the highest swing from Labour to Conservative in the 2010 general election.

Elections in the 2000s

Elections in the 1990s

Elections in the 1970s

Elections in the 1960s

Elections in the 1950s

Elections in the 1940s

General Election 1939–40: Another general election was required to take place before the end of 1940. The political parties had been making preparations for an election to take place from 1939 and by the end of this year, the following candidates had been selected;

• Conservative: Frances Davidson
• Liberal: Ian Davidson^[24]
• Labour: A W Harper^[25]

Elections in the 1930s

Elections in the 1920s

Elections in the 1910s