In 1887, John Bartholomew's Gazetteer of the British Isles described South of the Witham like this:
Witham, South of the, par., Lincolnshire, pop. 2.
The location is approximately that shown for "South of the Witham" in the Boston area enlargement on the 1888 Sanitary Districts Diagram for Lincolnshire, given its location relative to the boundary of Boston parish as overlaid by us on the New Popular OS map. The name has not been located on a topographic map, but the area appears to be between the straightened modern river and the loops of the old course.
A Vision of Britain through Time includes a large library of local statistics for administrative units. For the best overall sense of how the area containing South of the Witham has changed, please see our redistricted information for the modern district of East Lindsey. More detailed statistical data are available under Units and statistics, which includes both administrative units covering South of the Witham and units named after it.
GB Historical GIS / University of Portsmouth, History of South of the Witham, in East Lindsey and Lincolnshire | Map and description, A Vision of Britain through Time.
Date accessed: 25th November 2015
Click here for more detailed advice on finding places within A Vision of Britain through Time, and maybe some references to other places called "South of the Witham".