Need to import Federal holidays into your calendar?
Try finding them here: US Federal Holiday dates.
You can verify the dates manually at Federal Holidays Calendars from 1997 to 2010, the official U.S. government site.
Whatever you do, avoid CalendarData.com - I downloaded and imported an iCalendar from them without realizing that it was simply one person's homemade calendar. The bad feed had people's anniversaries, birthdays, and other nonsense, even though it was featured on the front page as "United States National Holidays".