The longest in terms of words was Jimmy Carter’s final message, in January 1981. A written document rather than a speech, the report was 33,667 words long.
The longest orally delivered speech (at least since they started tracking these things in 1966) was Bill Clinton’s January 2000 address, which clocked in at 1 hour, 28 minutes and 49 seconds. Incredibly, that speech was only 7,452 words long, not nearly as long as his 1995 talk, in which he jammed 9,190 words into 1 hour, 24 minutes and 58 seconds. That ’95 address, by the way, was the longest in terms of word count, delivered as a speech.
In the republic’s early days, the House and Senate debated the president’s message and sent formal replies back to him. That practice was eventually deemed too time-consuming and stopped. And while George Washington and John Adams gave their messages in the form of speeches, Thomas Jefferson stopped the practice. It wasn’t until Woodrow Wilson in 1913 that the State of the Union speeches restarted. In all, 76 out of 220 such messages have been delivered by the president, in person.
Two presidents–William Henry Harrison and James Garfield–never delivered such a message to Congress. Both died in office before they were able to.