Stephanie, Ya, I saw those maps. Those were the one's I was going by when I went to the Phila Genealogical Society to do research. They have a Pa book of map formations though, and it was a little different than what's online. I've been using both since then just to get an idea of the counties formed at what time. Thanks! Teri Teri, Have you checked this out: www.pagenweb.org/map/index.html? It contains maps of Pennsylvania county formation over time. It might narrow things down a little. And I believe most of the county sites in the PaGenWeb project have info about their county's formation-- exact dates, from what original county, etc. Stephanie