The 56 men who signed the Declaration of Independence didn't all sign it at the same time, and most of them didn't even sign it on July 4th, 1776. The actual 'official' signing was on August 2nd, 1776, when most of the 56 signers put their signature on the document. (Thomas McKean was the last one to sign is, and he didn't do so until January of 1777.)
Benjamin Franklin wanted to name the turkey as the national animal. Fortunately, John Adams and Thomas Jefferson were able to give the honor to the bald eagle.
Just for reference, when the United States officially became a country in 1776, there were about 2.5 million people living here. Today that number is around 300 million.
Independence Day hasn't always been a paid Federal holiday, or even an unpaid holiday for that matter. It wasn't until 1870 that Congress declared the 4th of July was a day off for Federal workers, but it was unpaid time off. It wasn't until 1941 that it became a paid day off.
The national anthem isn't exactly an original tune. It's actually sung to the tune of an old English drinking song called 'To Anacreon in Heaven'. (Of course, the anthem's lyrics weren't written until 1814, so it's not only quirky, it's got practically nothing to do with the 4th of July or the revolution.)
Speaking of songs, "Yankee Doodle" is (sort of) an American original, and it was sung around the time of the American Revolution.... by British military officers. The song was actually poking fun of the backwards, buckskin-wearing 'Yankees' they had fought with during the French and Indian War several years earlier.
Last year, the Unites States imported $190 million worth of fireworks from China... the bulk of the demand. Though there's no word on how much of that was specifically spent for 4th of July festivities, it's safe to assume the number is 'a lot'. (New York City uses about 20 tons worth of fireworks to celebrate Independence Day each year.)
Most of the US flags and 4th of July-related items are, ironically, made in China. About $350 million dollars are spent very year to import these flags and decorations.
Malia Obama, President Obama's daughter, was born on the 4th of July.