New Year's Day, January 1, has been a US federal holiday since 1870. When it falls on a Saturday the federal holiday is observed on Friday, December 31 of the year before, and on a Sunday it moves to Monday, January 2.
Yes. New Year's Day is one of the 11 US federal holidays, so federal offices, banks and post offices close.
Why does the date of New Year's Day change each year?
The date stays the same; only the weekday moves. A common year has 52 weeks and one day, so a fixed date moves one weekday later each year, and two after February 29.