When did corporate or government employment start to rule?

I'm not sure if this is the right place for this question, but I can't think of another right place. I think there was a time (maybe waaay back) when the majority of US workers were either self-employed or were employed by another individual, rather than by a corporation or government. I think today this is no longer true. In that case, I'd like to know when the tipping point was reached.