Kendall Harmon has been running a series of posts in T19 on Average Sunday Attendance (ASA) for various dioceses for the 1998-2008 period. I managed to find some older data on the ECUSA website going back to 1992, so I've created a couple of charts which examine this from a slightly different perspective.
Our first chart shows ASA by diocese as a percentage of 1992 ASA:
The bold red line is domestic ASA. The legend to the right shows the dioceses in order by 2008 increase/decline (right-to-left, top-to-bottom) so that S. Carolina is at the top and San Joaquin is at the bottom.
Our second chart shows percentage change on a year-by-year basis:
In this case I have omitted Navaholand and San Joaquin, the first due to its volatility and the second due to its extreme at the end. I've also omitted selected extreme values along the way for other dioceses. The heavy red line again shows overall domestic ASA changes.
Both of these show pretty much the same pattern: up until 2001, the church was holding its own, and in many places showing increases. From 2002 on, almost all dioceses show substantial losses. Of course, it's only going to be worse next year, as three more dioceses all but disappear.