The picture below is taken from the official programme of the event, published daily during racing.
I hope the Stewards will forgive me for breaching their copyright, since thismap is very useful for showing the various historical markers along the boomed Henley course. The total distance is 1 mile 550 yards exactly, which is 2112 metres.
The stations are named Bucks and Berks, and the river flows against the course,so if the locks are opened more, times will be slower, and the Bucks station will be more disfavoured. Times in the programme are given to the Barrier(just after the Quarter-Mile), to Fawley, which is around half-way up the course, and to the finish.
The Henley Women's Regatta is run 2 weeks before the Royal, and uses the first 1500 metres of the boomed course, though times are given in a more modern way over standard distance markers.
More information can be found online for Henley and the Royal Regatta and for Henley Women's Regatta. No information online is published for the Henley Veteran's Regatta which takes place a week after the Royal.