Is chickenpox still prevalent in the us?

Yes. Mostly, new cases have decreased: that's incidence , and is due to the vaccine.
Declined but present. The incidance of chickenpox has declined about 85% from introduction in 1995 to 2004. That translates nationwide to a drop from 2 million down to 300, 000. See aap/redbookvaricella-zoster.