Kendall Harmon has posted a set of links to The Episcopal Church (TEC)'s membership & attendance numbers from 2002 and 2009.
2002 is significant because that was the year that the Diocese of New Hampshire announced an actively homosexual man as a candidate for bishop. 2009 is the last full reporting year for church stats.
Although the candidate was not actually elected until 2003, and not consecrated as a bishop until 2004, his 2002 nomination had people sounding warnings and started some toward the exits.
There were three main groups sounding warnings:
1. People who could not in conscience support so great a departure from the church's historic belief and practice.
2. People who were willing to talk about change, but did not believe that the denomination was ready to make such a move.
3. People of various positions on LGBT issues who believed that such a move would damage relationships with other Christians.
The warnings, singly and in combination, were ignored.
In 2002, TEC membership was at just over 2.3 million, with average Sunday attendance (ASA) at 846,640.
By the end of 2009, membership had fallen to barely over 2 million, with ASA down to 682,963.
The numbers are probably worse because TEC continues to count as members/attenders some congregations that have disaffiliated from the denomination.