Is it illegal to lie to the police?
In Illinois there is a charge called obstructing identification. It is a form of obstructing justice.
This podcast episode was encouraged by the Illinois criminal court case of People v. Schronski, 2014 IL App (3d) 120574 (07/09/2014).

So When is Illegal to Lie to the Police?
In this version of the law, it is a crime to lie to the police about your name. However, it is not absolutely against the law and it is only illegal to lie to the police under certain circumstances.
To sustain a conviction for obstructing identification, the prosecution must prove that a person:
(1) Intentionally or knowingly provided a false or fictitious name, residence address, or date of birth to a peace officer; and
(2) Was either:
(a) lawfully arrested or detained, or
(b) the information was requested from an individual that was reasonably believed to have witnessed a crime.
See 720 ILCS 5/31-4.5(a).
See also other Illinois Crimes in this handy crimes index.
Obstructing Identification is Unique
The thing that is different about this crime is that the prohibited conduct is not always technically illegal.
Example
What I mean is that some acts are just illegal no matter what. Killing someone is murder, always. Sure there is such a thing as self defense. But self defense is a way to excuse behavior we still generally try to prohibit. A self defense claim does not change the fact that the law tries to prevent a killing by criminalizing the act in the first instance.
Lying to Police
The act of lying to the police is not always meant to be prohibited by the criminal law in the first instance. The law only wants to ban lying to the cops under certain circumstances. When it comes to your name, the law criminalizes (and thus tries to prevent) lying when your are lawfully arrested, detained, or when you are a witness to a crime.
The law does not take a position on lying to police about your name outside the realm described above.
So, Is It Illegal to Lie to the Police? Not Always
Say a cop is walking through a neighborhood and is just trying to get to know the members of the community.
If the officer came upon you and asked you your name trying to get to know you better. Giving a fake name, under these circumstances, is not illegal. The law takes no position on whether you should or should not lie to the officer.
This means every time a person is charged with obstructing identification, the questions that has to be asked is if:
(1) The person was a witness to a crime, and if
(2) The person was lawfully detained or arrested?
If the answer is “no”, the charge can be challenged in court.
This Feels Like a Search & Seizure Case
Often, the answer to the question, “Is it illegal to lie to the police?”, will turn on the legality of the arrest or detention.
This is the very same issue that frequently comes up when analyzing the legality of a police search or seizure.
So, a very similar analysis for the crime of obstructing identification will unfold.
To determine if it is illegal to lie to the police, one looking at the case critically would then look at the type of police-citizen encounter that transpired.
Types of Police-Citizen Encounters
Police-citizen encounters are generally limited to three circumstances:
- An arrest supported by probable cause;
- A brief investigatory stop based on a reasonable and articulable suspicion of criminal activity; and
- An interaction for purposes of community caretaking or public safety.
Convincing a judge or jury that the police did not make a valid arrest or investigatory stop could mean an acquittal.
Community caretaking encounters do not involve coercion or detention and therefore do not rise to the level of a seizure under the fourth amendment. A detention occurs when a reasonable, innocent person in the circumstances would believe that he or she would not be free to leave. Thus, if the judge or jury believes that the police were only interacting with the person in community caretaking function would also mean victory in court.
Lying to the Police is a Fluid Beast
The crime of obstructing identification is a fluid beast. It means sometimes the act of lying to the police is a crime and sometimes it is not.