I guess it all depends on what you mean by illusory, right? I wrote all of these articles while working for a nondual philosophy blog, so I'm happy to take the counter-perspective on this. However, Oxford philosopher Galen Strawson has a great and very easy-to-understand refutation of free will:

(1) Nothing can be causa sui - nothing can be the cause of itself. (2) In order to be truly morally responsible for one's actions one would have to be causa sui, at least in certain crucial mental respects. (3) Therefore nothing can be truly morally responsible.

http://www.informationphilosopher.com/solutions/philosophers/strawsong/