(Note that I decided to research these numbers based on the preceding post about the bishop of the diocese–KSH).
According to the U.S.Census Bureau’s figures, Springfield, the see city of the diocese, has grown in population from 152,082 in 2000 to 153,060 in 2010. This represents a population growth of approximately 0.6% in this time frame.
According to Episcopal Church statistics, the Diocese of Western Massachusetts went from Average Sunday Attendance (or ASA) of 7,295 in 2000 to 5,208 in 2010. This represents a decline of 28.6% during this decade.
Please note that if you go to the link toward the end of this sentence and enter “Western Massachusetts” as the name of the diocese and then “View Diocese Chart” underneath on the left you can see in pictorial form some of the data from 2000-2010.