In my rust belt diocese, there were parishes every few blocks, mostly ethnic. Today the diocese has closed almost half of the parishes in the last 20 years. There still are lots of parishes with under 200 people attending on the weekend, mostly elderly. The outer suburbs have a few enormous parishes, because the diocese put a freeze on new parishes since 1970 due to the priest shortage (and because they feared the opposition to closing iconic neighborhood parishes).
The problem is people fight tooth and nail to keep open those huge old churches, where grandmother got married, where many relatives were baptized, etc. Many of these buildings are genuinely historic structures, but there is no money to keep them up.
There is a desperate need for the diocese to put more priests, and more money, into outreach in the suburbs to youths, and especially, young adults. That is really part of our Catholic heritage that has been forgotten, as much as I would like to keep beloved old St X parish open.