This is one of my favorite maps of religion. It was produced by Glemary research, and it shows the predominant religious affiliation in counties nationwide. It demonstrates the many historical patterns that shaped American religion. For example, you can see the westward path of the Methodist circuit riders (in green) plus the immigration of Northern Europeans to the Northern Midwest.
Patheos Explore the world's faith through different perspectives on religion and spirituality! Patheos has the views of the prevalent religions and spiritualities of the world.