It seems like subculture, especially among youth, has been much more popular in the last few decades then ever before. Is that true? When people look back at Beatniks, Flappers, and Bohemians it always seems like the modern imagination of old-timey cities that are bursting at the seams with underground culture might be a little exaggerated.
Would the general population have been very aware of subcultures, in the way that most people now could describe the look and music of b-boys, hipsters, goths, burning man hippies, and punks? Does the influence that subcultures seem to have on art and music mean that they are more interesting to study in proportion to how many of them there actually were? Were there subcultures in places and times that haven't made it into American pop culture's view of history?
I answered a slightly similar question before that you might check out
Subcultures, though the term is anachronistic, did exist before the mid 20th century, but in general they can be assumed to be smaller. The vision of subcultures as bursting at the seams isn't necessarily wrong, but the United States (which is the only case I know well) was a much more normative culture, so when subcultures did get attention it was more to condemn them than to promote them. So the notion that they were everywhere is questionable, but cities (predominantly ports or major trade hubs) were definitely bastions of difference rather than all merely the same. It's hard to say how much different it is from today because it depends on where you draw lines between "subcultures."
The reason for the explosion of subcultures in the 2nd half of the 20th century has a lot to do with the development of communications and transportation infrastructures (and market capitalism's push to render Americans into consumers); rural and suburban communities began to receive more information about different cultural forms via television, radio, and print (among other media). Newspapers and magazines had been accessible to the middle classes, of course, since the mid/late 19th centuries; these media also circulated ideas to rural/suburban folk, who may have taken up particular elements that they identified with, mimicked them wholesale but in radically different socioeconomic contexts, or been scandalized by them (or remained indifferent).
So, since the end of the civil war, people would have been able to be aware of subcultures; if they were or not depended a lot on where they lived, how they engaged with the developing mass public in the United States, and what "stake" they had in the particular subculture (if it would be well received within their community or not). What did they look like?
I don't quite understand your second to last question, but the answer to your last question is, as I think I've shown, yes.
Want to know more? The literature is HUGE on cultural history (which stretches much beyond my answer to your question, and which I could speak more about if you have specific questions). But here are some greatest hits that I've selected specifically before 1950. They aren't "subcultures" in the sense that you talk about -- that's a postwar phenomenon, and I've included Dick Hebidge's book on the topic. Indeed, a lot of them are "cultures" in their own right. They are in no particular order.
Hope this helps -- and I'm always curious to know what brings you to ask the question.