I specialize in German Genealogy and all of the records that I have in my family tree pertain to Koppenhoefer's in the Rheinland-Palatinate. Once I get all of my data transferred to my new computer, I'll take a look to see if any of them immigrated to the U.S. Koppenhoefer is the most common spelling in the area (with or without the 'e', in which case the 'e' is replaced by an Umlaut).