Cambridgeshire was, for a long time, effectively two separate counties: Cambridgeshire itself and the Isle of Ely, which comprised the hundreds of Ely, Wisbech and North and South Witchford.
This map shows the county of Cambridgeshire with its hundreds c. 1845.
And the map below shows the parishes in the same period, arranged by Hundred. (Click on the image for the full-sized version).
Sources: Victoria County History of Cambridgeshire; Historic Parishes of England & Wales, Roger J. P. Kain & Richard Oliver (2001).