Holiday’s name is self-evident: It’s the date on which it falls
You are free to parade, grill, engage in pyrotechnics, and otherwise celebrate Independence Day, but don’t feel it necessary to call it that.
The celebration of the nation’s birthday has the distinction of being the only official holiday named for a date rather than a person or event. There is a temptation to write it as the more descriptive and proper sounding “Independence Day,” but the holiday was originally known by the date on which it falls.
The Oxford English Dictionary records a reference in a diary to “Independence Day” in 1791. A Google Book search shows “Independence Day” was in use before Congress established July 4 as a day off in 1870. But the 1870 act, which made July 4 an unpaid day off for federal workers in the District of Columbia, called it “the fourth day of July.” So did the act that extended the day off to all federal workers in 1875.
Those acts referred to all holidays as dates, but descriptive language was included for some of the holidays, as in “the twenty-fifth day of December, commonly called Christmas day.” There was no such description of the holiday that fell on the fourth day of July. In 1938, Congress decided to make “the Fourth of July” and other holidays paid days off.
The first Congressional reference to “Independence Day” appears to be a 1959 act that makes Friday, July 3, a paid day off, describing the holiday as “Independence Day (July 4).” The portion of the U.S. Code that deals with paid federal holidays now lists “Independence Day,” but it’s not clear when the name was first included.
The Associated Press Stylebook allows for Independence Day, July Fourth, or Fourth of July. It may give the impression that it has a preference, but this will vary depending on which you look up first. All are acceptable.
A search of Google’s Ngram Viewer, which searches Google’s book database for frequency of terms, shows “Fourth of July” more commonly used than “Independence Day.” Use of “Independence Day” has been steadily rising in Ngram Viewer’s American corpus since around the 1850s and was more common in books in the late 1990s, but “Fourth of July” has since regained top status.
In the spirit of the holiday, then, we can call our day off whatever we like.
I’d be remiss if I didn’t note here that it is incorrect to describe July 4 as the day the Continental Congress voted for independence. Richard Henry Lee’s resolution that the “United Colonies are, and of right ought to be, free and independent States” was adopted on July 2, 1776. The letter to King George spelling out the reason why was adopted two days later.
Following the lead of the founders, I now submit these facts to a candid world.