Ordnance Survey Maps of England and Wales - Revised: Kent illustrates the parish boundaries of Kent when rural districts were still in existence and before Greater London came into being. The map publication year is 1931. An earlier map of 1900 may also be useful. The maps blow up to show all the parishes and many of the small villages and hamlets. Maps in this series are now downloadable for personal use.
Steve Archer has produced a very useful round-up of the available census records for Kent - and where/from whom they are available.
Registration Districts in Kent for the period 1837 to the present. By drilling down through the links you can follow any parish through the registration districts to which it was attached.
Bishop's Transcripts for Kent parishes, 1558-1887, can be found on FamilySearch since February 2016
The Kent Family History Society and the North West Kent Family History Society are the most dominant, but there are also
Volume 2 of the Victoria County History of Kent (published 1926) is available online through the auspices of British History Online. It includes accounts of the early history of Canterbury and Rochester cathedrals, and of several sites now within the conurbation of London.