I've been doing a little research about the first Thanksgiving for a lesson I'm teaching, and I thought it might be fun to share a few details.
The first Thanksgiving was celebrated on December 12th, 1621 in Plymouth Colony. The reason for the feast was two-fold. The last of the colony's harvests had just come in, and for the first time, the often starving colonists felt that they had a bounty. The second reason was a visit from "King" Massasoit, an important leader of a nearby native tribe. A colonist named Edward Winslow reported on the feast:
Our corn [i.e. wheat] did prove well, and God be praised, we had a good increase of Indian corn, and our barley indifferent good, .... Our harvest being gotten in, our governor sent four men on fowling, that so we might after a special manner rejoice together after we had gathered the fruit of our labors. They four in one day killed as much fowl as, with a little help beside, served the company almost a week. At which time, amongst other recreations, we exercised our arms, many of the Indians coming amongst us, and among the rest their greatest king Massasoit, with some ninety men, whom for three days we entertained and feasted, and they went out and killed five deer, which they brought to the plantation and bestowed on our governor, and upon the captain and others. And although it be not always so plentiful as it was at this time with us, yet by the goodness of God, we are so far from want that we often wish you partakers of our plenty.