If you can find the part of town your ancestors lived in, using the Census, you might be able to narrow down the Catholic churches.
Here is a page I used:http://www.rootsweb.ancestry.com/~kylgs/sources.html
It tells you when the church was established and were the records exist now, Very helpful.
I located some ancestor records by faxing a letter with the names, dates, I had. It takes some follow-up and much of the work is done by volunteers.