The nation has celebrated the birth of its first president since 1885. But since Congress moved the holiday to the third Monday of February in 1968, it has been colloquially known as Presidents’ Day. That’s partly because Abraham Lincoln’s birthday is Feb. 12, but the official holiday is “Washington’s Birthday.” Interestingly, George Washington was actually born on Feb. 11, 1731, according to the then-used Julian calendar. The 1752 adoption of the Gregorian calendar shifted his birth date to Feb. 22, 1732.