George Washington was not a huge fan of celebrating his birthday.

A diary entry on his 28th birthday, Feb. 22, 1760, reveals a busy day installing a fence around the peach orchard at Mount Vernon, his home in Virginia.

As Alexis Coe, a presidential historian and Washington biographer, put it, “He would be more apt to chronicle the weather on his birthday than any present he received — unless it was a mule.”

And yet nearly 300 years after his birth, many Americans will have the third Monday in February off to honor the first president of the United States. (This year, that falls on Feb. 20.)

Colloquially known as Presidents’ Day in a nod to the birthdays of Abraham Lincoln and other past presidents, the federal holiday officially celebrates only Washington’s Birthday.

The story of how it became a three-day weekend is steeped in differing calendars, inconsistent punctuation, labor issues and, of course, politics.

For the first 20 years of his life, Washington celebrated his birthday on Feb. 11, the day he was born in 1731, according to the then-used Julian calendar. But the date of Washington’s birthday moved in 1752, when the British Parliament adopted the newer Gregorian calendar to reflect a more accurate length of the solar year (it’s complicated). As a result, all earlier dates were shifted by one year and 11 days.

In all of her years of researching Washington, Ms. Coe, the author of “You Never Forget Your First: A Biography of George of Washington,” said she had never come across any reference to “an obligatory or regular family birthday.”

But by 1778, as Washington was leading the Continental Army against the British, his vision for what a birthday celebration could mean for a new country began to change. When he and his men were stationed at Valley Forge in Pennsylvania, a group of drummers and fifers celebrated his birthday with a performance in front of his quarters.