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 Oregon, the criminal offense of unlawful assembly is addressed under ORS 166.025, which defines 'Disorderly conduct in the second degree.' According to this statute, a person commits the offense if, with intent to cause public inconvenience, annoyance or alarm, or recklessly creating a risk thereof, they engage in conduct including, but not limited to, obstructing vehicular or pedestrian traffic, or refusing to disperse when ordered by a law enforcement officer in the context of an assembly of three or more persons which threatens public order. The law also covers making unreasonable noise, fighting, or engaging in violent, tumultuous, or threatening behavior. Unlawful assembly in Oregon may overlap with other offenses such as rioting, but it is specifically addressed within the context of disorderly conduct. Violation of this statute is classified as a Class B misdemeanor. It's important for individuals to understand that while the right to assemble is protected by the First Amendment, assemblies must be peaceful and not infringe upon the rights of others or disrupt public order.