I think more interesting stuff is not mythical roots of this ideology, but why the English Whig tradition became so "influential" that it obliterated the traditions of cooperation, guilds and trade unionism other immigrant groups (e.g. Germans or Scandinavians) brought to this country?
My impression is that individualism was a relatively marginal ideology until the government-sponsored explosion of the suburban sprawl in 1950s. There is an obvoious "elective affinity" between suburban lifestyles on the one had and romantic individulaism (popularized by Hollywood, esp' "wild west" genere) on th eother.
Thus the quetsion we need to ask is: "what is the role of people who call themselves federal government in spreading of individualistic ideology?"
wojtek