The traditional "first Thanksgiving" was held in 17th century America by the Pilgrims (1621).
George Washington instituted a national day of Thanksgiving in 1789, but the event did not gain widespread official acceptance until Abraham Lincoln issued a proclamation on October 3, 1863, setting aside the last Thursday of November as a day of thanksgiving.
Incidentally, this proclamation was issued just a few weeks before Lincoln gave his famous address at Gettysburg (November 19, 1863).
Every president after Lincoln continued the Thanksgiving Day tradition, and Congress adopted the fourth Thursday of November as a national holiday in 1941.
The fourth Thursday can be as early as Nov. 22, and as late as Nov. 28. Formula: to determine the date of Thanksgiving next year: subtract one from the date this year; then if next year is a leap year, subtract 1 more. If that result is less than 22, add 7.
Robert C. Maher, Ph.D., P.E.
Montana State University
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