Jefferson County, MO Noise Ordinances: Decibel Limits (2026)

Section 400.3720 of the Unified Development Ordinance, adopted by Ordinance No. 26-0203 in 2026, sets the noise ceiling for data center operations measured at the property line. Daytime hours run 7:00 a.m. to 10:00 p.m. with a 55 dBA ceiling and a 65 dBC low-frequency ceiling; nighttime hours run 10:00 p.m. to 7:00 a.m. with the limit dropping to 50 dBA and 60 dBC. Those numbers apply whenever the adjoining parcel is zoned or used residential, whether or not a dwelling currently sits on it, or is institutional or agricultural with a dwelling; where the adjoining parcel is used or zoned for something else, the operator gets a 5-decibel cushion on both figures. Tonal, impulsive or rhythmic noise, meaning any sound carrying pure tones, rhythmic oscillation or an identifiable low-frequency hum, is treated as three decibels louder than the meter reads for enforcement purposes.

Before the County issues a construction permit, the applicant has to submit a 3D acoustic model built to ISO 9613-2 or an equivalent standard, covering the worst-case scenario of a summer peak day paired with nighttime operation, showing impacts at every property line and the nearest residences, and listing proposed mitigation with quantifiable decibel reductions; County staff can require a peer review of that model at the applicant's expense. Emergency generators may run only during actual outages or scheduled testing, testing is confined to weekdays between 10:00 a.m. and 4:00 p.m. outside holidays, capped at sixty minutes per generator per month, never run under load, and the generator housing itself has to cut noise by at least 25 dBA. By comparison, other outdoor conditional uses in the County, such as gun clubs and shooting ranges under Section 400.3210, cap out at a flat 65 dBA at the property boundary with no day/night split.