I don't have any statistical evidence to back this up, but many congregations in my area are slowly shrinking. The main reason for the shrinkage is the exodus of the young people. There is one congregation that is almost entirely full of people 30+, mostly with no children, and most of the capable brothers are 50+. So there are brothers in their sixties carrying the microphones because there just aren't any younger males. I hate to see the old guys shuffling around, half-awake trying to deliver the microphones, but it must happen. This particular congregation is in a relatively small Kingdom Hall, so the shrinkage isn't as visibly apparent.
There is another congregation in a much larger hall that looks completely deserted because of all of the early departures. They have even had to get elders shipped in from other congregations. When you go to one of their Thursday night meetings, you wonder if you are in the right place because there just isn't anybody there. The same six or ten people answer all of the Watchtower questions.
Because the territory isn't producing any more recruits, these two congregations will end up extinct within the next few years, probably swallowed whole by some of the larger congregations in adjoining territories.
Strangely enough, the congregations that are doing well are the ones where many of the publishers and elders are financially well off. The parking lots are full of pricey SUVs, Mercedes-Benz, Audis, and other vehicles as they try to keep up with one another in vehicles and house sizes. But since they can't really one-up one another in home size or vehicle price anymore (they are all about even), now they try to outdo each other with their vacations. Still, their Kingdom Halls stay packed. I don't know why unless they somehow they feel like they are going to miss something if they don't show up.
If you are new to the congregation and you are not able to keep up with them financially when they have their outings (shopping sprees, vacations, Saturday trips out of town, etc), you are going to be left out.
I don't know how I got so far off-topic.
Anyway, back to the point - I have noticed that many, many congregations are shrinking and it's not due to people moving away.