The federal holiday we know today as Thanksgiving was established by Congress in 1941, but American thanksgiving celebrations date all the way back to the time of the Pilgrims.
This post at a Library of Congress blog has a helpful summary of the history of the Thanksgiving holiday in the United States. The Library of Congress website also provides access to some great primary source material related to Thanksgiving. Be sure to check it out.
Happy Thanksgiving!
Ryan Wentzel