1950–1974 • The Urban Districts of
Bushey,
Chorleywood, and
Rickmansworth; and • The
Rural District of Watford.
The constituency was formed from the Watford Division of Hertfordshire, excluding the part comprising the Municipal Borough of Watford. It also included the parishes of Abbots Langley and Sarratt, transferred from Hemel Hempstead. 1974–1983 • The Urban Districts of Bushey, Chorleywood, and Rickmansworth; and • The Rural District of Watford civil parishes of Abbots Langley, Sarratt, and Watford Rural.
The parish of Aldenham in the Rural District of Watford was transferred to the new constituency of
South Hertfordshire.
1983–1997 • The District of Three Rivers wards of Ashridge, Bedmond, Carpenders Park, Chorleywood, Chorleywood West, Croxley Green, Croxley Green North, Croxley Green South, Hayling, Langleybury, Maple Cross and West Hyde, Mill End, Money Hill, Moor Park, Northwood, Oxhey Hall, Rickmansworth, and Sarratt; and • The District of Dacorum wards of Berkhamsted Central, Berkhamsted East, Berkhamsted West, Bovingdon and Flaunden, Chipperfield, Kings Langley, and Northchurch.
The parts of the District of Dacorum, including Berkhamsted, were transferred from the abolished constituency of Hemel Hempstead. Abbots Langley was transferred to Watford and Bushey to the new constituency of Hertsmere. 1997–2010 • The District of Three Rivers wards of Ashridge, Chorleywood, Chorleywood West, Croxley Green, Croxley Green North, Croxley Green South, Hayling, Maple Cross and West Hyde, Mill End, Money Hill, Moor Park, Northwood, Rickmansworth, and Sarratt; and • The District of Dacorum wards of Aldbury and Wigginton, Berkhamsted Central, Berkhamsted East, Berkhamsted West, Bovingdon and Flaunden, Chipperfield, Northchurch, Tring Central, Tring East, and Tring West.
Gained Tring from the abolished constituency of West Hertfordshire. Kings Langley transferred to a re-established Hemel Hempstead, Bedmond to St Albans, and three further wards in the Three Rivers District to Watford. 2010–2024 • The District of Three Rivers wards of Chorleywood East, Chorleywood West, Croxley Green, Croxley Green North, Croxley Green South, Hayling, Maple Cross and Mill End, Moor Park and Eastbury, Northwood, Penn, Rickmansworth, Rickmansworth West, and Sarratt; and • The District of Dacorum wards of Aldbury and Wigginton, Berkhamsted Castle, Berkhamsted East, Berkhamsted West, Bovingdon, Flaunden and Chipperfield, Northchurch, Tring Central, Tring East, and Tring West.
Minor gain from Hemel Hempstead following revision of local authority wards. Current Further to the
2023 Periodic Review of Westminster constituencies, which came into effect for the
2024 general election, the composition of the constituency is as follows (as they existed on 1 December 2020): • The Borough of
Dacorum ward of Kings Langley. • The entire District of
Three Rivers. The constituency saw major changes with the bulk of the portion of the previous iteration of seat in the Borough of Dacorum, including the towns of
Berkhamsted and
Tring, forming part of the newly created constituency of
Harpenden and Berkhamsted. The Bovingdon, Flaunden and Chipperfield ward went to
Hemel Hempstead in exchange for the
Kings Langley ward. The parts of the District of Three Rivers not previously within the constituency were transferred primarily from
Watford, with a small area from
St Albans. Only 55% of the electorate of the former constituency remained in the redrawn seat, and only 63% of the redrawn seat's electorate came from the previous version of the constituency ==Members of Parliament==