Searching for a map of Luxembourg settlement patterns (a long story), I stumbled across this interactive map of immigrant settlements created in 2009 by The New York Times. The map allows you to see where immigrants were living at different times by selecting for time periods and countries. The information is based on historic census dated.
Unfortunately, there's no option for Luxembourgers. You can use Germany as a second - Luxembourgers are often mislabeled as German on the census - but beware. You'll be getting data from other German speaking countries mixed in. And our ancestors didn't have a huge amount in common with settlements in Pennsylvania. It's interesting but not a great research tool. Has anyone found a better option?