Originally Posted by JDR13
Not sure of the exact origin, but I'm pretty sure Steampunk is a lot older than Mad Max. I don't think the term became common until the late 80s or early 90s though.

Steampunk mostly originated from work by SF/Fantasy authors Tim Powers and Blaylock (James?) in the 80s.

Edit:
Just looked at Wikipedia and it was actually coined by K W Jeter:

It was coined by science fiction author K. W. Jeter, who was trying to find a general term for works by Tim Powers (The Anubis Gates, 1983), James Blaylock (Homunculus, 1986), and himself (Morlock Night, 1979, and Infernal Devices, 1987)

Should have remembered Jeter was a part of it in some way, given that I have both of the books mentioned.