# List of Hertfordshire boundary changes

Boundary changes affecting the English county of Hertfordshire. The county borders Buckinghamshire to the west, Bedfordshire and Cambridgeshire to the north, Essex to the east and Greater London to the south. Until 1965 it had a southern boundary with Middlesex it continues to have a boundary with Middlesex. It was the administrative Middlesex County Council that was abolished not the historic County of Middlesex. This was confirmed in 2011 by the United Kingdom Government.

## Summary

Apart from a number of minor exchanges of land with surrounding counties, the alterations in Hertfordshire's boundaries involved the following:
* The county had four exclaves that were integrated into their surrounding counties in 1844, and a set of six small enclaves of Bedfordshire was annexed.
* In the south, the boundary with Middlesex was somewhat complex, with Hertfordshire forming a long protrusion into it. In 1889 Hertfordshire gained some territory in this area and when Greater London was formed in 1965 the whole area, including Barnet and East Barnet, became part of the new county. Potters Bar in Middlesex was surrounded by Hertfordshire on three sides, and it was transferred to it in 1965, along with South Mimms.
* In the north, the town of Royston was partly in Cambridgeshire until 1896
* In the north west there were various irregularities in the boundaries with Buckinghamshire and Bedfordshire which were adjusted in the years from 1883 to 1897.
* In the south west the growth of the towns of Chorleywood and Rickmansworth necessitated an adjustment of the boundary with Buckinghamshire in 1906.
* More recently, the boundary with Greater London has been partially aligned to the M25 motorway.

## List of changes

| Date | Legislation | Effect |
| 20 October 1844 | Counties (Detached Parts) Act 1844 | Coleshill (part) transferred to Buckinghamshire Meppershall (part) transferred to Bedfordshire Studham (part) transferred to Bedfordshire Shillington (part) transferred from Bedfordshire (six small enclaves) -listed on schedule as Ickleford in error |
| 25 March 1883 | Divided Parishes and Poor Law Amendment Act 1882, Local Government Board Order 19622 | Parts of Drayton Beauchamp and Marsworth transferred from Buckinghamshire |
| 25 March 1885 | Local Government Board Order 16585 | Part of Edlesborough (Hudnall) transferred from Buckinghamshire |
| 24 March 1888 | Local Government Board Order 21701 | Part of Edlesborough transferred from Buckinghamshire |
| 1 April 1889 | Local Government Act 1888 | Monken Hadley parish and parts of Enfield and South Mimms parishes transferred from Middlesex |
| 30 September 1895 | Local Government Board Order P 1170 | The parish of Nettleden and part of the parish of Ivinghoe transferred from Buckinghamshire |
| 30 September 1896 | Local Government Board Order P 1173 | The part of the parish of Royston in Cambridgeshire transferred from Cambridgeshire to become North Royston parish Part of Bassingbourn parish transferred from Cambridgeshire to become South Bassingbourn parish Part of Kneesworth parish transferred from Cambridgeshire to become South Kneesworth parish Part of Melbourn parish transferred from Cambridgeshire to become South Melbourn parish |
| 31 September 1896 | Local Government Board Provisional Orders Confirmation (No. 13) Act 1896 | South Mimms (part) transferred from Middlesex |
| 30 September 1897 | Local Government Board Order P 1312 | Humbershoe and part of Houghton Regis transferred from Bedfordshire to Hertfordshire to form the new parish of Markyate |
| 30 September 1897 | Local Government Board Order P 1313 | Part of Shillington parish transferred from Bedfordshire to Hertfordshire |
| 1 October 1900 | Local Government Board Order 41337 | Parts of the Buckinghamshire parish of Ashley Green exchanged with parts of parishes of Bovingdon and Northchurch, Hertfordshire. |
| 1 April 1907 | Counties of Bedford and Hertford (Alteration of County Boundaries) Order 1906 | Parts of parishes of Caddington, Hyde and Studham transferred from Bedfordshire Parts of parishes of Flamstead, Harpenden Rural and Markyate transferred to Bedfordshire |
| 1 April 1907 | Counties of Buckingham and Hertford (Alteration of County Boundaries) Order 1906 | Exchanges of small unpopulated areas: between the Buckinghamshire parishes of Ashley Green, Chalfont St Peter, Chenies, Denham, Gerrards Cross, Hawridge and Latimer with the Hertfordshire parishes of Chorleywood, Northchurch, Rickmansworth Rural and Wigginton |
| 1 October 1926 | Ministry of Health Provisional Orders Confirmation (No. 10) Act 1926 | Minor exchanges between Ridge, Hertfordshire and South Mimms, Middlesex and Shenley, Hertfordshire and Hendon, Middlesex |
| 18 September 1934 | Ministry of Health Declaration under section 145 of the Local Government Act 1933 (Alteration of Watercourses) | Realignment of boundary with Essex due to alteration of watercourses. |
| 1 April 1935 | The County of Hertford Review Order (Ministry of Health Order No. 80168) The County of Essex Review Order (Ministry of Health Order No. 83994) | Transfer of small areas of Eastwick and Gilston to Essex |
| 28 September 1947 | Ministry of Health Declaration | Part of Arlesey transferred from Bedfordshire |
| 13 August 1956 | Ministry of Health Declaration | Part of Arlesey transferred from Bedfordshire |
| 1 April 1965 | London Government Act 1963 | Potters Bar Urban District gained from Middlesex Former area of Barnet Urban District and East Barnet Urban District transferred to Greater London |
| 1 April 1989 | The Cambridgeshire, Essex, Hertfordshire and Lincolnshire (County Boundaries) Order 1989 | Transfers from South Cambridgeshire to North Hertfordshire (mainly to Royston parish) |
| 1 April 1993 | The Greater London and Hertfordshire (County Boundaries) Order 1992 | Southern part of Elstree village from Barnet/Harrow to the Elstree and Borehamwood parish in Hertfordshire Some streets on the edge of Barnet town gained by Barnet from unparished area of Hertsmere, Hertfordshire |
| 1 April 1993 | The Essex and Hertfordshire (County Boundaries) Order 1992 | Changes to Essex/Hertfordshire boundary |
| 1 April 1994 | The Essex, Greater London and Hertfordshire (County and London Borough Boundaries) Order 1993 | Changes to the Greater London/Hertfordshire boundary: some alignment to the M25 motorway |