Analyzing data from the 2020 U.S. Religion Census shows interesting patterns in religious diversity in the United States and the Chicago region. First, a map of religious diversity across all groups:

There is a good amount of diversity across counties with this measure. The Chicago area is in the middle, leaning toward less diversity by this measure.

Second, putting together all of the Christian traditions under one umbrella leads to a different map of diversity:

The Chicago region is now more diverse with the metropolitan counties generally on the side of more diversity.

Third, a map of different religious traditions:

This helps show the ways the Chicago region is diverse with a number of religious traditions present. Find county by county findings here.

The article has a summary of the larger patterns across the United States:

But if we regard Christianity as a single monolith — lumping all the Catholics, Presbyterians, Methodists, Lutherans and whatnot in one big sacramental wine jug — we find that the most religiously diverse places in America are generally the big cities. The urban Northeast leads the pack.

That’s because if America has a Quran Belt, a Torah Belt or a Bhagavad Gita belt, greater New York City forms its buckle. Almost half of America’s Jews, by synagogue adherence, live in either New York or New Jersey — which also happen to be the second and third most Islamic states, after Illinois. And they’re in the top three for Hindu Americans (along with Delaware). The Buddhists stick to the West Coast (and D.C.).

In other words, religious diversity varies quite a bit by county in the United States with metropolitan regions tending to be more diverse. The Chicago region is in the middle and has a large presence of Catholics.