I grew up in that part of the world. Practically everyone was either German or Czech and Catholic, or German or Scandinavian and Lutheran.
I was thinking specifically of the French Jesuits whose missions in the 1600's were to the Indians and settlers in the upper reaches of the US and Southern Canada. Other etnic varieties of Catholics moved in later. I knew that Illinois and the Midwest had lots of German and Czech Catholics, and there are lots of Polish Catholics in Chicago. Many of the Catholics in central MA and in NY are of French Canadian origin, though the Boston area is more heavily Irish.
Which is why my spelling is bad, but I can pronounce names with 14 consonants and two vowels!