taking bits from previous posts:
How many people identify themselves as Homebrewers - 22K, the number of AHA members
How many people have homebrewed - 750K
The actual number is probably somewhere between these two - and maybe on the lower side. There are a lot of active homebrewers who don't belong to a club or to the AHA (I belong to both). There are probably also a lot of folks who would say they are a homebrewer, but have really only tried it a few times - or perhaps haven't brewed in a very long time. And then there are those who do the brew-on-premise thing. Are they home
The 750K number is almost certainly high. There are about 300 million people in the USA. By the time you consider that about 30-35% of Americans over 18 don't drink alcohol, then factor out children, the infirm, incarcerated or otherwise incapacitated and most women (I'm not trying to be sexist - it just seems that the overwhelming majority of homebrewers are men), 750K is probably a little over 1% of the potential available population. That may not seem like a lot - but it is - probably more than probability would account for.
A good analogy might be cycling. A lot of us can ride a bicycle. A lot of us own a bicycle - maybe more than one. However, how many would actually refer to themselves a cyclist? It probably depends who you're talking to, and what purposes the numbers server for them. There's an old saying that goes "figures lie, and liars figure." I'm not suggesting that the AHA or any other group lies about their numbers, but I think it's good to try to keep things in perspective.