The First National Thanksgiving Proclamation was signed by George Washington, the first President of United States on 3rd October 1789 during his first year as President and it set aside Thursday, November 26 as “A Day of Public Thanksgiving and Prayer.”
Entitled “General Thanksgiving,” the First National Thanksgiving Proclamation appointed the day “to be observed by acknowledging with grateful hearts the many and signal favors of Almighty God.”
Although there were Thanksgiving observances in America before the Washington’s proclamation, this Thanksgiving Proclamation represents the first to be so designated by the first national government.
Later, on October 3, 1863, President Abraham Lincoln issued a proclamation calling for the observance of the fourth Tuesday of November as a national holiday of Thanksgiving.
In 1939, President Franklin D. Roosevelt moved the holiday to the third Thursday of November but after a storm of protest, Roosevelt changed the holiday again in 1941 to the fourth Thursday in November, where it stands today.
Anyways, please find below the text of First National Thanksgiving Proclamation of George Washington.
The First National Thanksgiving Proclamation
Proclamation of National Thanksgiving
City of New York, October 3, 1789
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.”
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, for the great degree of tranquility, 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.
And also that we may then unite in most humbly offering our prayers and supplications to the great Lord and Ruler of Nations and beseech him to pardon our national and other transgressions, to enable us all, whether in public or private stations, to perform our several and relative duties properly and punctually, to render our national government a blessing to all the people, by constantly being a Government of wise, just, and constitutional laws, discreetly and faithfully executed and obeyed, to protect and guide all Sovereigns and Nations (especially such as have shown kindness unto us) and to bless them with good government, peace, and concord. To promote the knowledge and practice of true religion and virtue, and the encrease of science among them and Us, and generally to grant unto all Mankind such a degree of temporal prosperity as he alone knows to be best.
Given under my hand at the City of New York the third day of October in the year of our Lord 1789.