Is this for 2021? Have you already filed your 2021 tax return?
What state (if any) is shown in box 15 of the W-2 for the health insurance opt-out? If it's not IL, what makes you say that the W-2 is from IL?
Do you work in AL? Did you also receive a W-2 for your regular salary with AL in box 15?
Are the employer's name and EIN the same on both W-2s?
It’s for an opt out on health insurance but “salary” is indicated on the form.
Where on the W-2 does it say "salary"?
Is the employer who issued the W-2 based in Illinois?
Did you actually (physically) work in Illinois?
We need a bit more detail in order to answer your question correctly.
Q. Do I put this on my Al taxes or file a separate IL return?
A. Simple answer: both. But, you need to explain more, particularly what does "received a w-2 from IL" mean?
The general rule is: your report all your income on your home state return, even the income earned out of state. You file a non-resident state return for the state you worked in and pay tax to that state. Your home state will give you a credit, or partial credit, for what you paid the non-resident state.
Taxable fringe benefits are treated as salary for taxes purposes. That's why you got a W-2. But, if you live and work in AL, IL tax should not have been withheld. You may have to file an IL return only to get a refund. The income will be taxed on your AL return, regardless of how you handle IL. If no IL was withheld, you do not need to file an IL return.