One of my colleagues in the Lords, knowing that Donald Trump was to be inaugurated as President of the USA on Friday, asked if the inauguration was determined by the day (Friday) or the date (20 January). It is the date. George Washington was inaugurated in April 1789, but thereafter – up to and including 1933 – the President was inaugurated on 4 March. Since 1937, the date has been 20 January. If 20 January falls on a Sunday (as it did in 2013), the President is sworn in by the Chief Justice in a private ceremony, with a public ceremony the following day.
The longest inaugural address – lasting nearly two hours – was given by William Henry Harrison in 1841. At 68, he was the oldest President to be elected (until Ronald Reagan and now Donald Trump) and it was a bitterly cold day. He caught a cold and is generally believed to have contracted pneumonia. Some sources have argued that he had a bacterial infection. In any event, he fell ill and died a month later, the first President to die in office.
The inauguration ceremony normally takes place on Capitol Hill but on occasion, as when a Vice-President succeeds a President who has died, it has occurred elsewhere and the oath administered by someone other than the Chief Justice. Lyndon B. Johnson (1963) was famously sworn in by District Judge Sarah T. Hughes and the only President to be sworn in aboard an aircraft. Calvin Coolidge (1923) was sworn in by his father, a notary public. Franklin Roosevelt is the only President to be sworn in more than twice, having been elected to four terms, though dying shortly after being sworn in for his fourth term, propelling his new Vice-President, Harry S Truman, into the White House. The Constitution was subsequently amended to prevent a President being elected to more than two terms.