The Cartographic Department of the National Archives in Adelphi MD has enumeration district maps for various counties in various census years. There are outlines of the township boundaries. Clarendon county maps are available for at least 1930 & 1910 and perhaps other years, I just do not recall.

You can also search the census rolls. There is a series that lists the enumeration district descriptions as well, that would help somewhat in approximating township boundaries.

Good luck,
Damita Drayton Green
dldgreen@mail.com