Porn isn't illegal under 18 in anywhere in the United States. The law is there to control kids (this is a factual statement, that came from the cops).
I talked to police when they raided me for my kiddy pr0n picture that I accidentally acquired (and uploaded to the internet to ask my friend if it was real or photosh00p'd), and in the mean time I asked them two questions:
1. Why do cops like donuts?
and
2. Is porn illegal under 18?
Answer to #1: They like donuts because late at night, not much is open when it comes to food except for Dunkin' Donuts.
Answer to #2: It's not illegal, no one is going to kick your ass for looking at porn. But it has to be YOUR OWN WILL, to go on the websites / torrents / your grandpa's secret porn stash. If someone gives it to you, there's going to be an issue. Otherwise, if you yourself look at porn on the internet... no one is going to go after you.
Considering that many people look at porn under 18, I don't think it's really that big of an issue. Then again, these cops are New York cops, and where I live cops don't give a fuck about much. They said themselves (verbatim): "Porn in itself is not illegal"