RALEIGH, N.C. (WNCN) — Thanksgiving is a week away, and millions of Americans are heading to the grocery stores to prepare for their feasts on that Thursday.

Thanksgiving always falls on the fourth Thursday of November — but why?

According to the Old Farmer’s Almanac, we don’t know the actual day on which the Pilgrims celebrated the first Thanksgiving in 1621, though we know it took place in mid-October instead of November.

The Old Almanac states that beginning in 1668, Nov. 25 was the “legal” day of Thanksgiving, but that only lasted five years.

According to the Old Almanac, Thursday may have been designated “to distance the event from the Sabbath day among the Puritan colonists.” It also states that Thursday was also a lecture day in New England and ministers would give sermons every Thursday afternoon.

Then, during George Washington’s first term as president, he proclaimed Thursday, Nov. 26, 1789, as a “Day of Publick Thanksgivin” in honor of the new U.S. Constitution. Later, in 1863, according to the Old Almanac, Abraham Lincoln proclaimed the national day of Thanksgiving to be the last Thursday of November.

That changed to the second to last Thursday in 1939, during the presidency of Franklin D. Roosevelt, who in his effort to boost the economy, set out to create more shopping days before Christmas, according to The Almanac.

Nevertheless, people kept celebrating the holiday on the last Thursday of the month. The fourth Thursday in November was finally established in 1941 when Thanksgiving became a federal holiday.