• On Sept. 28, 1789, just before leaving for recess, the first Federal Congress passed a resolution asking that the president recommend to the nation a day of thanksgiving.
• On Oct. 3, 1789, President George Washington issued a proclamation naming Thursday, Nov. 26, 1789, as a "Day of Publick Thanksgivin" — the first time Thanksgiving was celebrated under the new Constitution.
• Washington proclaimed, in part, that the people of the United States would "to the service of that great and glorious Being, who is the beneficent Author of all the good that was, that is, or that will be—That we may then all unite in rendering unto him our sincere and humble thanks—for his kind care and protection of the People of this Country previous to their becoming a Nation—for the signal and manifold mercies, and the favorable interpositions of his Providence which we experienced in the course and conclusion of the late war—for the great degree of tranquillity, union, and plenty, which we have since enjoyed—for the peaceable and rational manner, in which we have been enabled to establish constitutions of government for our safety and happiness, and particularly the national One now lately instituted—for the civil and religious liberty with which we are blessed; and the means we have of acquiring and diffusing useful knowledge; and in general for all the great and various favors which he hath been pleased to confer upon us."
• Subsequent presidents issued Thanksgiving Proclamations, but the dates and even months of the celebrations varied. It wasn't until President Abraham Lincoln's 1863 Proclamation that Thanksgiving was regularly commemorated each year on the last Thursday of November.
• In 1939, the last Thursday in November fell on the last day of the month. Concerned that the shortened Christmas shopping season might dampen the economic recovery, President Franklin D. Roosevelt issued a Presidential Proclamation moving Thanksgiving to the second to last Thursday of November.
• As a result of the proclamation, 32 states issued similar proclamations while 16 states refused to accept the change and proclaimed Thanksgiving to be the last Thursday in November.
• For two years, two days were celebrated as Thanksgiving — the president and part of the nation celebrated it on the second to last Thursday in November, while the rest of the country celebrated it the following week.
• To end the confusion, Congress decided to set a fixed date for the holiday. On Oct. 6, 1941, the House passed a joint resolution declaring the last Thursday in November to be the legal Thanksgiving Day. The Senate, however, amended the resolution, establishing the holiday as the fourth Thursday, which would take into account those years when November has five Thursdays. The House agreed to the amendment, and President Roosevelt signed the resolution on Dec. 26, 1941, thus establishing the fourth Thursday in November as the federal Thanksgiving Day holiday.
Sources: The National Archives; The Papers of George Washington, Presidential Series, vol. 4, 8 September 1789 – 15 January 1790, ed. Dorothy Twohig. Charlottesville: University Press of Virginia, 1993, pp. 131–132.].