At what age is a teenager in the state of Illinois able to be involved in sexual course without getting police involved?

The age of consent in Illinois is 17.

It is also illegal for a person to commit sexual acts on a person under the age of 18 if he/she has a position of authority or trust over the victim.

(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.

Sec. 12-16. Aggravated Criminal Sexual Abuse. ...(d) The accused commits aggravated 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 at least 5 years older than the victim.