| The tradition of the Pilgrims' first Thanksgiving is steeped in myth and legend. Few people realize that the Pilgrims did not celebrate Thanksgiving the next year, or any year thereafter, though some of their descendants later made a "Forefather's Day" that usually occurred on December 21 or 22. Several Presidents, including George Washington, made one-time Thanksgiving holidays. In 1827, Mrs. Sarah Josepha Hale began lobbying several Presidents for the instatement of Thanksgiving as a national holiday, but her lobbying was unsuccessful until 1863 when Abraham Lincoln finally made it a national holiday with his 1863 Thanksgiving Proclamation.
The year that is drawing towards its close, has been filled with the blessings of fruitful fields and healthful skies. To these bounties, which are so constantly enjoyed that we are prone to forget the source from which they come, others have been added, which are of so extraordinary a nature, that they cannot fail to penetrate and soften even the heart which is habitually insensible to the ever watchful providence of Almighty God.
In the midst of a civil war of unequaled magnitude and severity, which has sometimes seemed to foreign States to invite and to provoke their aggression, peace has been preserved with all nations, order has been maintained, the laws have been respected and obeyed, and harmony has prevailed everywhere except in the theatre of military conflict; while that theatre has been greatly contracted by the advancing armies and navies of the Union.
Needful diversions of wealth and of strength from the fields of peaceful industry to the national defense, have not arrested the plough, the shuttle, or the ship; the axe had enlarged the borders of our settlements, and the mines, as well of iron and coal as of the precious metals, have yielded even more abundantly than heretofore. Population has steadily increased, notwithstanding the waste that has been made in the camp, the siege and the battle-field; and the country, rejoicing in the consciousness of augmented strength and vigor, is permitted to expect continuance of years with large increase of freedom.
No human counsel hath devised nor hath any mortal hand worked out these great things. They are the gracious gifts of the Most High God, who, while dealing with us in anger for our sins, hath nevertheless remembered mercy. It has seemed to me fit and proper that they should be solemnly, reverently and gratefully acknowledged as with one heart and voice by the whole American People. I do therefore invite my fellow citizens in every part of the United States, and also those who are at sea and those who are sojourning in foreign lands, to set apart and observe the last Thursday of November next, as a day of Thanksgiving and Praise to our beneficent Father who dwelleth in the Heavens.
And I recommend to them that while offering up the ascriptions justly due to Him for such singular deliverances and blessings, they do also, with humble penitence for our national perverseness and disobedience, commend to his tender care all those who have become widows, orphans, mourners or sufferers in the lamentable civil strife in which we are unavoidably engaged, and fervently implore the interposition of the Almighty Hand to heal the wounds of the nation and to restore it as soon as may be consistent with the Divine purposes to the full enjoyment of peace, harmony, tranquility and Union.
Abraham Lincoln
Lincoln's Thanksgiving Proclamation taken from the collection of Lincoln's papers in the Library of America series, Vol II, pp. 520-521
Today, our Thanksgiving is the fourth Thursday of November. This was set by President Franklin D. Roosevelt in 1939 (approved by Congress in 1941), who changed it from Abraham Lincoln's designation as the last Thursday in November (which could occasionally end up being the fifth Thursday and hence too close to Christmas for businesses).
But the Pilgrims' first Thanksgiving began at some unknown date between September 21 and November 9, most likely in very early October. The date of Thanksgiving was probably set by Lincoln to somewhat correlate with the anchoring of the Mayflower at Cape Cod, which occurred on November 21, 1620 (by our modern Gregorian calendar--it was November 11 to the Pilgrims who used the Julian calendar).
Courtesy of www.mayflowerhistory.com | 
