I think I'm looking for the same family. The German COPE lineage (PA,NC,IL,MO) was founded by one Yost Cope. Of course that is the english phonetic spelling. I am assuming that Koepp and Cope are pronounced the same? Yost hails from the Baden and Wuerttemburg region of Germany, he was born circa 1700 and immigrated to philadelphia in 1727. He travelled from Rotterdam aboard the "Adventure". He is listed as Joost Coope.
If I can break through the language gap and link Cope to Koepp I will let you know.