The short answer, of course, is that Congress says it is. In 1941, Congress decreed that Thanksgiving should be held the fourth Thursday of November. Congress was formalizing the Thanksgiving-on-Thursday that had been observed annually across the nation since 1863. In 1863, Abraham Lincoln, in the midst of the Civil War, implored Americans to give thanks for the good that could be found despite the terrors of war and strife, in a national holiday to be held the last Thursday of November.
Why did Lincoln choose Thursday? Most historians point to precedents set by the Continental Congress and by George Washington. The Continental Congress declared the first nationwide day of Thanksgiving as Thursday, December 18, 1777 (after the Battle of Saratoga). George Washington issued a proclamation in 1789, the first year of the United States' existence, decreeing Thursday, November 26 to be the first National Thanksgiving. But why did theychoose Thursday?
Up to that point, there had been a long tradition of individual colonies declaring days of Thanksgiving. Of course, the Pilgrims of Plymouth Colony celebrated Thanksgiving. The first Thanksgiving is generally believed to have taken place in the fall of 1621, but we have scant evidence of it. The Thanksgiving of 1623 is better documented, but was held in July. The first "proclaimed" Thanksgiving was held in Charlestown, Massachusetts Bay Colony on June 29, 1676, on a Monday. Other colonial proclamations such as the 1721 Connecticut Thanksgiving held on November 8, a Wednesday, were not terribly consistent in terms of when they were held (although most were held in the fall, at harvest time).
The most likely source of influence for the choice by the Continental Congress and by George Washington of the Thursday Thanksgiving is colonial governor Jonathan Belcher (1682-1757), who served as governor of Massachusetts Bay Colony from 1730 to 1741, and as governor of New Jersey from 1747 to 1757. In 1730, Belcher issued a proclamation decreeing Thursday, November 12, 1730 as a day of Thanksgiving. In 1749, in New Jersey, he again issued a proclamation of Thanksgiving for Thursday, November 23, 1749. There are many similarities between this proclamation and the proclamation issued by Washington in 1789. (Belcher had many friends, allies, and acquaintances who were friends, allies, or acquaintances of Washington and other Founding Fathers.)
It should come as no surprise to our local supporters that Belchertown, just up Route 181 from the farm, is named in honor of Governor Belcher, who owned a great deal of land in the town of Cold Spring, which was renamed Belcher's Town when it was officially incorporated in 1761.
So, if you like your four-day weekend because Thanksgiving falls on Thursday, thank Governor Jonathan Belcher!
(For a history of Belchertown, visit http://www.belchertown.org/departments/history/bhistory.htm. For more about Belcher's Thanksgiving decrees, visit http://www.belcherfoundation.org/thanksgiving_day.htm.)