“Privacy”, at least the modern legal understanding of it, goes back to Griswold v. Connecticut. At the time(1965?) Connecticut forbid the sending of birth control information through the mail. The Supreme Court found that Connecticut mail receivers had a reasonable expectation that the state would not be opening their mail.
As I recall(a bit hazily), GvC was one of the building block for Roe v. Wade.
Yes, but the funny thing is that I believe the Court later ruled that your bank records were not private because you had no expectation of privacy when you stood at the teller window and deposited cash. Go figure.