The most obvious answer could be “Yes”, yet not all of us are part of a group, many can say they are. Even if the group is a friend, it’s a group, right? Well, in a strict way of thinking, you can think of groups as subjective abstract circles, or objectives ones. That is, circles of people (think of Google+ circles, maybe?), made around you, by you and for you, which you are part of, or circles made not by one, not for one, but by many, for many. objective circles are “stablished” social groups; subjective circles are “improvised” social groups.
So, in a way, you, as a person, living around people, are part of a big social group, made by the city/town, in which social interacting is set to a minimum, letting society exist. Get that? From that, every one of us usually makes circles, or rings, that catch other people into our mental environment, setting social interaction to what we specify, on our part, and what they specify, on theirs.