The criminal offense of unlawful assembly generally means the assembly of multiple persons resulting in conduct that (1) is intended to commit a breach of the peace or other unlawful act; (2) creates an immediate danger of damage to property or injury to persons; (3) substantially obstructs law enforcement or other governmental functions or services; (4) is tumultuous or violent and likely to cause public alarm; or (5) deprives any person of a legal right or disturbs any person in the enjoyment of a legal right by using force or the threat of force.

Unlawful assembly laws vary from state to state and some states have related offenses such as rioting, riots and routs, participating in a riot, inciting a riot, failing to disperse, and disturbing the peace. The criminal offense of unlawful assembly may be included in the definition of one or more of these offenses or may be a separate criminal offense. These laws are generally located in a state’s statutes—often in the penal or criminal code.

In Missouri, the criminal offense of unlawful assembly is addressed under Missouri Revised Statutes, specifically in Chapter 574 which deals with offenses against public order. Unlawful assembly in Missouri is defined under Section 574.040, where it is considered a crime for seven or more persons to assemble and agree to violate the laws related to felonies or misdemeanors involving the use of force or violence, and to act towards the execution of that agreement. This statute covers situations where the assembly could lead to a breach of peace or pose a danger to persons or property. Missouri law also includes related offenses such as rioting and failure to disperse. A riot is defined under Section 574.050, where it involves seven or more persons acting with the intent to violate any of the laws of the state or to prevent or hinder the execution of any legal process. The offense of failure to disperse, under Section 574.060, occurs when six or more persons are gathered and causing a public alarm, and at least one person refuses to obey the lawful order of law enforcement to disperse. Penalties for these offenses can range from misdemeanors to felonies, depending on the circumstances and the presence of aggravating factors.