Became a federal holiday in 1870
It was not until 1870 that Thanksgiving became a federal holiday. President and former Union general Ulysses S. Grant signed an act into law establishing federal holidays.
There were four days set aside as federal holidays in the 1870 bill. In addition to Thanksgiving, the legislation also listed Christmas, Independence Day and New Year's Day.
The legislation was meant to give federal employees who lived in the District of Columbia time off, with an 1885 bill expanding some of the holidays to include all federal workers.
According to a 2021 report by the Congressional Research Service, Thanksgiving's official date was not fixed but rather would be observed "either on the last Thursday in November or the first Thursday in December, with one exception."