Hertfordshire is a county lying to the north of Greater London. It includes suburban and commuter towns whose residents work in London. It is also the location of a number of new towns developed to host "overspill" population from the capital.
In 1965, under the London Government Act 1963 parts of Hertfordshire were included in Greater London and the London Borough of Barnet. At the same time, Potters Bar was transferred to Hertfordshire from the abolished county of Middlesex.