The Continental Congress issued the first American Thanksgiving proclamation on Nov. 1, 1777.
Here is the text of that proclamation:
Forasmuch as it is the indispensable duty of all men to adore the superintending providence of Almighty God; to acknowledge with gratitude their obligation to him for benefits received, and to implore such farther blessings as they stand in need of; and it having pleased him in his abundant mercy not only to continue to us the innumerable bounties of his common providence, but also smile upon us in the prosecution of a just and necessary war, for the defense and establishment of our unalienable rights and liberties; particularly in that he hath been pleased in so great a measure to prosper the means used for the support of our troops and to crown our arms with most signal success:
It is therefore recommended to the legislative or executive powers of these United States, to set apart Thursday, the 18th day of December next, for solemn thanksgiving and praise; that with one heart and one voice the good people may express the grateful feelings of their hearts, and consecrate themselves to the service of their divine benefactor; and that together with their sincere acknowledgments and offerings, they may join the penitent confession of their manifold sins, whereby they had forfeited every favor, and their humble and earnest supplication that it may please God, through the merits of Jesus Christ, mercifully to forgive and blot them out of remembrance; that it may please him graciously to afford his blessings on the governments of these states respectively, and prosper the public council of the whole; to inspire our commanders both by land and sea, and all under them, with that wisdom and fortitude which may render them fit instruments, under the providence of Almighty God, to secure for these United States the greatest of all blessings, independence and peace; that it may please him to prosper the trade and manufactures of the people and the labor of the husbandman, that our land may yield its increase; to take schools and seminaries of education, so necessary for cultivating the principles of true liberty, virtue and piety, under his nurturing hand, and to prosper the means of religion for the promotion and enlargement of that kingdom which consisteth in righteousness, peace and joy in the Holy Ghost.
And it is further recommended, that servile labor, and such recreation as, though at other times innocent, may be unbecoming the purpose of this appointment, be omitted on so solemn an occasion.