Most federal holidays are clear-cut. On the Fourth of July, for example, Americans celebrate the adoption of the Declaration of Independence in 1776. On the other hand, Presidents Day is a slightly strange holiday for three main reasons:
There is no universal agreement on the actual name of the holiday.
There is no universal agreement on which presidents are being honored.
There is no agreement on something as simple as whether is an apostrophe in "presidents."
Ask a handful of people who the holiday is meant to recognize, and you aren't likely to get the same answers. In fact, what is generally called Presidents' Day is still recognized by the U.S. government as Washington's Birthday. USA.gov lists it like this: George Washington's Birthday (Presidents Day) -- February 17 and it describes the holiday this way:
"Washington's Birthday is observed the third Monday of February in honor George Washington, the first President of the United States. This date is commonly called Presidents Day and many groups honor the legacy of past presidents on this date.
Some states do in fact honor both Washington, who was born Feb. 22, and Abraham Lincoln, who was born Feb. 12. But other states honor Washington and Thomas Jefferson, but not Lincoln, on this holiday and some states honor all the presidents. Then there are a handful of states, including Illinois, that have declared Lincoln's birthday a state holiday -- whatever day of the week Feb. 12 happens to fall -- while also marking the federal holiday. In Virginia, Washington's home state, the holiday is called George Washington's Day. In Alabama, it is called "Washington and Jefferson Day" (although Jefferson was born on April 13)."
How did this holiday come to be ?
Washington's actual birthday, Feb. 22, became a U.S. government holiday back in 1885. In the early 1950s, there was a movement led by a coalition of travel organizations to create three-day weekends by moving the celebration of some holidays to Mondays. One of the suggestions was to create a Presidents Day between Washington's birthday and Lincoln's birthday, which was a holiday in some states. A few states tried the new arrangement, but it was not universally adopted across the country. Also in the early 1950s there was a proposal to make March 4 -- the original presidential inauguration day -- a holiday to honor all presidents, but that went nowhere.
The National Holiday Act of 1971 passed by Congress created three-day weekends for federal employees by moving the celebration of some holidays to Mondays, although states did not have to honor them.
So, today, though the federal holiday is marked on the third Monday in February, there is no agreed-upon name, no universal agreement on who is being celebrated, and the use of the apostrophe in the name is varied: Sometimes it isn't used at all (as in Presidents Day), sometimes it is placed between the last two letters (President's Day) and sometimes it is after the last letter (Presidents' Day).
Put all this together, and it seems fair to see that Presidents' Day, or President's Day, or Presidents Day, is a slightly strange holiday.