The Chicago Gang Congregation Ordinance, which prohibited criminal street gang members from loitering in public places, was found to be unconstitutional by both the Illinois Supreme Court and the US Supreme Court. The ordinance was deemed invalid due to its vagueness, which made it an arbitrary restriction on personal liberties. The law did not restrict speech or any conduct intended to convey a message, and it infringed on an individual's right to loiter for innocent purposes, which is protected by the Due Process Clause of the Fourteenth Amendment. The vagueness of the ordinance may invalidate it for failing to provide notice of what conduct it prohibits or for authorizing arbitrary and discriminatory enforcement. As a criminal law that contains no mens rea requirement and infringes on constitutionally protected rights, the Chicago ordinance is subject to facial attack. The lower court's ruling was affirmed.

The Gang Congregation Ordinance of Chicago has been deemed unconstitutional by the Illinois Supreme Court due to its lack of clear guidelines for law enforcement and potential for arbitrary and discriminatory enforcement. The ordinance allows police officers absolute discretion and lacks minimal standards to guide their judgment, making it overly broad and vague. The requirement for prompt obedience to a dispersal order is also unconstitutionally vague. The U.S. Supreme Court cannot impose a limiting interpretation of the ordinance if the state court has declined to adopt it. However, there are reasonable alternatives available to address the real threat of gang violence and intimidation, such as laws that target only gang members or incorporate limits on enforcement. The Justice concurs in the judgment and joins Parts I, II, and V of the Court's opinion.

Justice Kennedy agrees with most of the Court's opinion and judgment, but he shares Justice Stevens' concerns about the Chicago ordinance's notice adequacy. He believes that the ordinance could criminalize innocent behavior and that the requirement to disobey a police order before violating the ordinance does not necessarily save it. The Court recognizes that some police orders may subject a citizen to prosecution for disobeying, even if the citizen does not know the reason for the order. However, any unexplained police order cannot be blindly obeyed without notice of its lawfulness. The Court finds that the predicate of an order to disperse is not sufficient to eliminate doubts regarding the adequacy of notice under the Chicago ordinance.

The ordinance in question allows police officers to order any person to leave any public location, with the exception of two limitations. However, the first limitation still leaves many individuals subject to its restrictions, and the second limitation gives police officers too much discretion to close off major portions of the city to innocent individuals. Therefore, the ordinance is unconstitutional in all its applications and cannot be applied to the defendants, even if they behaved poorly. The city may apply some other law to the defendants in light of their conduct, but it cannot apply this law to them as it is repugnant to the due process clause. Specification of details of the offense intended to be charged would not serve to validate it.

The Supreme Court upheld a Chicago ordinance that restricted citizens' freedom to loiter in public places due to criminal street gangs, finding it to be a minor limitation on freedom. The Court cannot declare a statute unconstitutional in all applications, only as applied to the person before it. The author criticizes the Court's decision to declare the ordinance facially invalid, arguing that the plurality's formula for facial invalidation is not a well-accepted formula in jurisprudence. The author disputes the "vagueness invalidates" rule proposed by the concurrences, arguing that it is unreasonable and impractical for modern urban society. The author argues that the criminal ordinance does have a mens rea requirement, as the actus reus of the ordinance is the failure to promptly obey an order to disperse, which must be accompanied by wrongful intent. The author contends that the ordinance is not vague, as it provides definitive standards that apprise persons of ordinary intelligence of the prohibited conduct and does not encourage arbitrary or discriminatory enforcement. The author argues that remaining in one place is not constitutionally protected, and therefore it is up to the citizens of Chicago to decide whether the tradeoff between the ordinance and individual liberties is worth it.

Justice Thomas dissents from the Court's decision to invalidate Chicago's anti-gang loitering ordinance, arguing that it is necessary to maintain public peace and disperse threatening groups. He disagrees with the plurality's reasoning that the freedom to loiter for innocent purposes is protected by the Due Process Clause. The author argues that the ordinance prohibiting loitering and vagrancy does not violate the Due Process Clause, as police officers have a duty to preserve public peace and prevent crime. They criticize the plurality's argument that there is a constitutional right to "loiter for innocent purposes" and suggest that the Court should not create new substantive due process rights without clear constitutional authority. The Court's conclusion that the ordinance is impermissibly vague cannot be reconciled with common sense, longstanding police practice, or Fourth Amendment jurisprudence.