the fourth Thursday of November (the United States)
The Pilgrims, who celebrated the first thanksgiving in America, were fleeing religious prosecution (政治迫害) in their native England. In 1609 a group of Pilgrims (英国清教徒) left England for the religious freedom in Holland where they lived and prospered. After a few years，they found the Dutch frivolous (肤浅的，无聊的) and their ideas a threat to their children's education and morality. So they decided to leave Holland and travel to the New World. It was agreed that the Pilgrims would be given passage and supplies in exchange for their working for their backers for 7 years. On Sept. 6, 1620 the Pilgrims set sail for the New World on a ship called the Mayflower.
The dangerous trip was cold and damp, took 65 days, during which many passengers became sick and one person died by the time land was sighted on November 10th.
They finally settled in Plymouth which offered an excellent harbor and they found the local Native American Indians a peaceful group.
With generous help of the native Indians, the survivors embraced their first harvest after their bitter struggle with the first harsh winter in Plymouth. Since the Pilgrims had much to celebrate, they had built homes in the wilderness, they had raised enough crops to keep them alive during the long coming winter.
The Pilgrim Governor William Bradford proclaimed a day of thanksgiving to be shared by all the colonists and the neighboring Native Americans.
However, the 3rd year brought a spring and summer that was hot and dry with the crops dying in the fields. Governor Bradford ordered a day of fasting and prayer, and it was soon thereafter that the rain came. To celebrate - November 29th of that year was proclaimed a day of thanksgiving. This date is believed to be the real true beginning of the present day Thanksgiving Day.
The custom of an annually celebrated thanksgiving, held after the harvest, continued through the years.In 1863 President Abraham Lincoln appointed a national day of thanksgiving. Since then each president has issued a Thanksgiving Day proclamation, usually designating the fourth Thursday of each November as the holiday.