History of parliamentary constituencies and boundaries in Essex

The ceremonial county of Essex, which includes the unitary authorities of Southend-on-Sea and Thurrock, has returned 18 MPs to the UK Parliament since 2010. As a result of the creation of Greater London under the London Government Act 1963, which came into effect on 1 April 1965, the boundaries of the historic/administrative county were significantly altered, with the south-western corner, representing a majority of its population and seats, being transferred to Greater London, forming the London Boroughs of Newham, Barking and Dagenham, Havering, Redbridge and Waltham Forest.

Source: Wikipedia — History of parliamentary constituencies and boundaries in Essex (CC BY-SA 4.0)