I'm not sure it changed in a way that matters so much. You have 2 necessary groups you need to survive: the close mutual help group, people who will actually turn up at your funerals, wedding, help your kids if you die, shits like that. And you have the group of people you need to discuss things, change your opinion, teach you things, buy and sell to/from you.
So you want to talk "before", so let's say 1850 to go far enough.
For the first group, the affective partnership group, you had your family, often large and extended, and a few friends you met along the way.
For the second group, the social need group, you had you childhood friends still living around, your village, the other farmers around you, your clients and your trading partners (animal food providers, if you raised animals, stuff like that).
Your community, an American concept we don't have in French (in French it has a religious/isolated meaning like a monastery, I feel we would rather say "village"), I suppose would be the second one. People who depends loosely on you and on which you depend loosely (but you can switch, there's no personal feelings if you stop contact with part of it etc).
A forums on the internet, if you're an at home programmer, for instance, will be the same. You need some of them now, they're like a group of traders in your village you use to get stuff for your own farm. Now if you dislike their pricing or advice, you can change forum just like you could look for another group in the village before.
In short, I think your mistake is to expect community members in the past would go to your funerals (well there was a sense of duty in a village to do it because church, but it didn't mean people would cry at it or deeply miss you). A family and friends, a concept that has existed forever and still exists to this day, would and will.
And if you're not a programmer, the internet might be a lot less important, it may be to discuss guns for instance, and have fun comparing and sharing experience. But I guess calling that a community is more a PR move by people trying to sell you a social aspect to an experience, rather than a proper usage of the word to describe what the concept is. I'd call it an online forum, which is what these things are (the word has this underlying "discussion" meaning, in a multicast way)