This is greyed out. I see the answer to go to system preferences/keyboard/ Nope. The "correct spelling" under keyboard/text is turned off. Next? Don't want to correct spelling sometimes in Fakebook and other places.
Mac mini (Late 2014), OS X El Capitan (10.11.4)
I figured it out. No, that wasn't the correct answer either.
The setting "can" be app specific. (Asterisk, may or may not apply, could or could not work, order now).
So, without any help or information from anywhere, using inituition since there are only 78,000 forums possibilities and suggestions ... if you are in Facebook, like I was, and if creating a post, RIGHT CLICK on the word and turn off "Correct automatically." I did the other two things suggested here and "correct spelling automatically" was greyed out. The only way to get to it was the way I just described.
Instead of System Preferences, go to your Safari menu bar, click Edit > Spelling & Grammar.
Select or deslect as needed.
How to disable autocorrect in Safari
