[Everglades]

Here is a chart to the state tinting regulations:

http://www.tintworld.com/images/AUTOMOTIVE-LAWS.pdf

Explanation of the chart is here:
http://www.tintworld.com/services/automotive-services/window-tinting/window-tint-regulations/

For cars, look in the columns "F. side" = Front, side; "B. side (Car)" = Back, side; and "Rear (car)" for the % of light that must be allowed to be pass through.

 

[srobinso11]

That chart is from 2001 and is wrong for Illinois. The law was changed back in 2009. Maybe some other states have changed their tint laws since then too...

http://www.tintcenter.com/laws/IL/

Edit: After briefly looking at the tintcenter website, 14 other states also have newer laws than 2001...

 

[mrblanche]

The law also changed in Texas this year.

 

[Screechymon]

Yeah, I'd be careful with the .PDF unless it's being updated frequently. However if I'm not mistaken, because it is a law, the information has to be accessible and up to date, I thought I saw an .org site than covered the US, Briefly looking I've not come across the site.

Either way, it's good to check your state laws before tinting your windows yourself.

Here in NY if you have your tints done by some one they make you sign a waver, basically stating you understand the tints are illegal if 70% of light doesn't come through.

One of those CYA notes.

 

[DrivenDaily]

When I had mine done the first time ever, they told me what the law was. A reputable shop will know the law and give you your choices.

 

[Silver LTZ]

Lots of that info is wrong. But it is a starting place I guess.