San Mateo County, CA Public Conduct: Loud Party Ordinance (2026)
Key Facts
- Scope
- Unincorporated area only
- Gathering size
- 4 or more people
- Minor age
- Under 21
- 3rd violation
- Liable for response costs
- Payment deadline
- 14 days of citation
Summary
In unincorporated San Mateo County, hosting a loud or unruly gathering of four or more people where a minor drinks, uses cannabis, or is served alcohol triggers social-host liability and fines.
No person shall act as a Social Host, as defined in Section 3.05.020 of this chapter, of a Loud or Unruly Gathering where a Minor has possessed, consumed, or has been served any Alcohol, Alcoholic Beverage, Cannabis, and/or Controlled Substances.(b)It is the duty of any Responsible Person who knowingly hosts, permits, or allows a gathering at any public or private premises to take all reasonable steps to prevent the possession and/or consumption of any Alcohol, Alcoholic Beverage, Cannabis and/or Controlled Substance by any Minor, as well as the service of these items to any Minor.(c)As used in this section, reasonable steps shall mean and include, but shall not be limited to:(1)Controlling access to Alcohol, Alcoholic Beverages, Cannabis and/or Controlled Substances;(2)Verifying the age of persons at the gathering by inspecting government-issued driver's licenses or identification cards; and(3)Supervising the activities of Minors at the gathering. (Ord. No. 04810, § 1, 2-26-2019)
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 47).
Full Breakdown
Chapter 3.05 applies only in the unincorporated county and bars anyone from acting as social host of a loud or unruly gathering, four or more people with excessive noise, street obstruction, public drunkenness, fights, vandalism, or litter, where a minor under 21 possesses, consumes, or is served alcohol, cannabis, or controlled substances. Hosts must take reasonable steps such as controlling access, checking ID, and supervising minors. The Sheriff enforces the chapter through administrative fines under Chapter 1.40, and a third or subsequent violation makes the host jointly and severally liable for the County's public-safety response costs.
Violations & Fines
Administrative fines under Chapter 1.40 apply to each violation; a third or later violation adds joint and several liability for police and fire response costs.
Frequently Asked Questions
Does this apply inside Redwood City or Daly City?
What counts as a 'loud or unruly gathering'?
Sources & Official References
Other rules in San Mateo County
California rules heatmap·Compare San Mateo County to another location·View the California public conduct overview
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