Flipping off a police officer in Illinois is not illegal. Courts in the United States, including federal appeals courts, have consistently ruled that giving the middle finger is a form of protected speech under the First Amendment—even when the gesture is directed at law enforcement. The Sixth Circuit Court of Appeals specifically stated that “any reasonable officer would know that a citizen who raises her middle finger engages in speech protected by the First Amendment,” and that such behavior is not grounds for a stop or arrest.
However, while flipping off a cop is not a crime, police officers may sometimes use broadly written disorderly conduct laws to detain or cite individuals, especially if the gesture is accompanied by additional behavior that could be seen as disruptive or threatening. In practice, arrests or citations for simply flipping off a cop are not legally justified, and any charges are unlikely to hold up in court.
You have a constitutional right to flip off a police officer in Illinois, but doing so may still attract unwanted attention or complicate your interaction with law enforcement. The gesture itself is protected speech, and you cannot be lawfully arrested or convicted solely for giving the finger to a cop.
Sources
[1] https://www.kopplawoffice.com/blog/2019/03/rude-gestures-protected-by-first-amendment/
[2] https://www.abajournal.com/news/article/flipping-the-bird-is-protected-by-the-first-amendment-federal-appeals-court-says-in-cop-stop-case
[3] https://967theeagle.net/is-it-illegal-to-give-a-cop-the-finger-in-illinois/
[4] https://www.talksonlaw.com/briefs/can-you-be-arrested-for-giving-the-finger-to-police
[5] https://www.findlaw.com/legalblogs/criminal-defense/do-you-have-the-right-to-flip-off-cops/
