This is an excellent question, and one I've wondered
about too. Over the years boroughs and townships have come
and gone and changed shape. If there is any published
work that describes this chronology, I've not heard of
one. There must be some county-based government organization
that can answer this question. I would start with
the Recorder of Deeds and see what they recommend.
Check http://www.chartiers.com/pages/muni.html for their
web address.