George Washington must have really liked the idea of having a national thanksgiving because when he became president, he established the first Thanksgiving as a national holiday. On 3 October 1789 President Washington proclaimed,
Whereas it is the duty of all Nations to acknowledge the providence of Almighty God, to obey his will, to be grateful for his benefits, and humbly to implore his protection and favor, and whereas both Houses of Congress have by their joint Committee requested me "to recommend to the People of the United States a day of public thanksgiving and prayer to be observed by acknowledging with grateful hearts the many signal favors of Almighty God especially by affording them an opportunity peaceably to establish a form of government for their safety and happiness.And thus, the November holiday was born. Another one was proclaimed by Washington in 1795, and then President Adams continued the tradition. It was that slacker, Thomas Jefferson who would let it totally slip his mind. Various presidents would continue to proclaim the holiday, and various states had it in their law books to observe it on a specific date. It wasn't until 1941 that Thanksgiving was had a designated annual date to celebrate.
Now therefore I do recommend and assign Thursday the 26th day of November next to be devoted by the People of these States 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...
Happy Thanksgiving citizens of the Colonies!