Area Support Groups (as far as I know) had nothing to do with security and "area governance" as you refer to but were large support/ log units. They became corps support groups and have now been re-named sustainment brigades.

Not sure who/ what was responsible for administering rear areas (from a governance perspective). The post-WW2 constabulary units come to mind but they were re-organized "cav" units (2d ACR/ CR is given credit for service as a constab unit). I think such elements were adhoc deals given to the senior commander in the area. You may want to begin your search of such efforts with post-WW2 constabulary units as well as precursors to civil affairs units.