Signed by Washington on October 3, 1789 and entitled "General Thanksgiving," the decree appointed the day "to be observed by acknowledging with grateful hearts the many and signal favors of Almighty God."
While there were Thanksgiving observances in America both before and after Washington's proclamation, this represents the first to be so designated by the new national government.
After their first harvest, the colonists of the Plymouth Plantation held a celebration of food and feasting in the fall of 1621. Indian chiefs Massassoit, Squanto and Samoset joined in the celebration with ninety of their men in the three-day event.
The first recorded Thanksgiving observance was held on June 29, 1671 [50 years later] at Charlestown, Massachusetts by proclamation of the town's governing council.
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.
In 1939, President Franklin D. Roosevelt moved the holiday to the third Thursday of November (to extend the Christmas shopping season and boost the economy). After a storm of protest, Roosevelt changed the holiday again in 1941 to the fourth Thursday in November, where it stands today.
History of Thanksgiving Day
Some interesting notes on the history of how the day came about: