It was coveted as an area easy to defend, and was controlled in the very early medieval period by the Gyrwas, an Anglo-Saxon tribe.

She afterwards founded a monastery at Ely, which was destroyed by Viking raiders in 870, but was rebuilt and became a famous Abbey and Shrine.

Following the Norman Conquest, the Isle became a refuge for Anglo-Saxon forces under Earl Morcar, Bishop Aethelwine of Durham and Hereward the Wake in 1071.

Troops from the garrison at Wisbech Castle were used in the siege of Crowland and parts of the Fens were flooded to prevent Royalist forces entering Norfolk from Lincolnshire.

The Horseshoe sluice on the river at Wisbech and the nearby castle and town defences were upgraded and cannon brought from Ely.

This temporal jurisdiction originated in a charter granted by King Edgar in 970, and confirmed by Edward the Confessor and Henry I to the abbot of Ely.

A chief bailiff was appointed for life by the bishop, and performed the functions of high sheriff within the liberty, who also headed the government of the city of Ely.

Under the Local Government Bill of 1888, which proposed the introduction of elected county councils, the Isle was to form part of Cambridgeshire.

Following the intervention of the local member of parliament, Charles Selwyn, the Isle of Ely was constituted a separate administrative county in 1889.

The county was small in terms of both area and population, and its abolition was proposed by the Local Government Boundary Commission in 1947.

Following the recommendations of the Local Government Commission for England, on 1 April 1965 the bulk of the area was merged to form Cambridgeshire and Isle of Ely, with the Thorney Rural District going to Huntingdon and Peterborough.