The answer is, unfortunately, more complicated than you might think.
Let's start by referring to the designated U.S. federal holidays, as listed by their official names on the USA.gov website:
New Year's Day - January 1
Birthday of Martin Luther King, Jr. - 3rd Monday of January
Washington's Birthday - 3rd Monday of February
Memorial Day - Last Monday of May
Independence Day - July 4
Labor Day - First Monday of September
Columbus Day - Second Monday of October
Veterans Day - November 11
Thanksgiving Day - 4th Thursday of November
Christmas Day - December 25
In total, there are ten federal holidays in the U.S. An eleventh, occurring only every four years, and only if it doesn't coincide with the Birthday of Martin Luther King, Jr., is Inauguration Day.
So those are all the federal holidays recognized by the U.S. government. But, guess what, unless you work for the federal government, this information has no direct relevance to you. You see, the federal government doesn't have the jurisdiction to establish holidays for anyone other than federal employees and for Washington, D.C.
Otherwise, in accordance with the U.S. Constitution, states reserve the power to designate their own holidays, hence why, if you refer to many states' official calendars of public holidays, you'll observe that they don't line up exactly with the federal calendar. Many state government offices in California, for example, are closed in official observance of Cesar Chavez day on March 31. A number of Southern states observe a Confederate Memorial Day, although the specific date varies by state. The religious holiday Good Friday is also officially observed in a number of states. Meanwhile, Columbus Day, although a federal holiday, is not observed (or at least not as a paid holiday) in an increasing number of states, including California, where it was eliminated, along with Lincoln's Birthday, as a state holiday by the Schwarzenegger administration in 2009. The matter of jurisdiction is also why Washington's Birthday is legally known by a number of different names, depending on the state, including Presidents Day, Presidents' Day, President's Day, Washington and Lincoln Day, George Washington/Thomas Jefferson Birthday, and George Washington's Birthday & Daisy Gatson Bates Day. Some states also observe a Presidents' Day holiday at a completely different time of year, while a number of states do not observe any variation of Washington's Birthday or Presidents Day at all.
Of course, unless you actually work for state government, still none of that directly pertains to you. The reality is that, in the U.S., the government, whether at the federal or state level, does not compel private businesses to close on any specified days. In other words, there are no true national holidays in the U.S., at least none in the sense of public holidays that all citizens are legally entitled to get off from work.
That said, in practice, the majority of employers in the U.S. do observe a number of holidays, usually following the federal schedule as a guideline. You should refer to your company's website or employee information handbook for specifics, but, as I mentioned yesterday, there are 6-7 what I call "major" or "real" holidays. These are the ones that allegedly the majority of employers observe:
New Year's Day
Day after Thanksgiving
As you can see, six of those days align with federal (and state) holidays, and those are the days that, according to the Society for Human Resource Management, over 90% of U.S. organizations observe. The seventh, the day after Thanksgiving, is arguably not a holiday at all, but about two thirds of organizations close that day (or else offer employees some sort of bonus compensation for their service).
I came to dub these 6-7 the "real" holidays, because, in my years of working for various different private organizations, these were the holidays that I consistently either got off from work (paid or not) or else was offered overtime pay to come in. This was as opposed to "fake" holidays, like Valentine's Day or Halloween, which might be met with festivities, but which did not get me out of having to work and were consequently without value to me.
I categorized Martin Luther King, Jr. Day and Veterans Day as "minor" or "semi-real" holidays. They were certainly real when I was a public school student and got those days off from class. But, in all my years working in the private sector, I never once was offered those days off (making them functionally "fake").
Presidents' Day is perhaps the only "semi-major" holiday. I've always gotten this day off, but apparently I've always been in the minority. Only about a third of organizations close operations that day—actually a slightly smaller number than on Martin Luther King, Jr. Day, and one that has declined over the decades.
As for Columbus Day, I consider that a "semi-fake" or "fake-ish" holiday, not only because it's controversial, but because, even when I was a public school student, it was inconsistent year-to-year whether I would get the day off.