This has already been covered but, yes, it is.
FTA:But under Illinois's age of consent laws, one person under the age of 17 can be charged with sexual abuse if he had sexual contact with another person under the age of 17, even if they're both the same age. Two 16-year-olds in a fully consensual relationship could be charged with abusing each other.
From the link in the article...
Actually, any voluntary sexual activity between two 16 year olds could put both of them on the sex offender registration list. Such sexual activity is a crime for which both could be prosecuted, if there was mutual sexual conduct because the “age of consent” has not been reached.
Illinois Age Of Consent Law:
720 ILCS 5/12-15) Sec. 12-15. Criminal sexual abuse. ...(c) The accused commits criminal sexual abuse if he or she commits an act of sexual penetration or sexual conduct with a victim who was at least 13 years of age but under 17 years of age and the accused was less than 5 years older than the victim.
Ok.
But they don’t bust 16 year old kids for sex.