Septic installation and replacement in Franklin County, Missouri
Franklin County is one of the biggest septic counties in Missouri: the county building department estimates there are between fourteen and a half and fifteen thousand private onsite systems here. It is also a county where the paperwork changed recently. The permit does not come from the health department, it comes from the Franklin County Building Department in Union, and the county replaced its onsite sewage ordinance with a version adopted in September 2025 that took effect on the first of October that year. Anything you were told about the process before that date is worth re-checking.
Who issues a septic permit in Franklin County, MO?
The Franklin County Building Department. That is the office to call before anything else, because in Missouri the permitting authority is not the same kind of agency in every county, and assuming it is the health department wastes a week in the counties where it is not.
Phone (636) 583-6384. Their page: Franklin County Building Department.
Source: Missouri Department of Health and Senior Services, onsite wastewater construction permit authority lookup for Franklin County, read 2026-08-26. Fees, forms and requirements change, and this county is the only current source for its own.
What does Franklin County require beyond the state standard?
- The county has its own onsite sewage ordinance: the County of Franklin On-Site Sewage Disposal Systems Ordinance and Regulations, adopted and amended on 23 September 2025 with an effective date of 1 October 2025. Source: Franklin County Building Department, read 2026-08-26.
- The Building Department issues the permits and inspects new construction within unincorporated Franklin County, so property inside an incorporated city may fall under that city instead. Source: Franklin County Building Department, read 2026-08-26.
- The county building department estimates that there are between 14,500 and 15,000 private onsite septic systems in Franklin County. Source: Franklin County Master Plan, read 2026-08-26.
- Parts of the unincorporated county are served by rural sewer providers, so a public sewer connection may be available where a homeowner assumes it is not. Source: Franklin County Master Plan, read 2026-08-26.
Missouri lets a county adopt standards more restrictive than the state's, so a requirement here is not evidence of the same requirement one county over.
Source: Missouri Department of Health and Senior Services, Onsite Wastewater Treatment, read 2026-08-26.
What is the ground like in Franklin County?
Franklin County is Ozark country with river alluvium along its northern edge, and no glacial till at all: the Missouri River forms the county’s northern border, which puts the whole county south of the glacial limit. The upland soils are loess over cherty limestone residuum, which is the profile that makes depth to bedrock and the seasonal water table the deciding factors rather than percolation rate alone. The Union soil series, which is common through the county uplands, was first established here in 1909.
That matters because the soil decides the system. A standard system needs at least one foot between the trench bottom and the limiting layer or seasonal high water table, rising to four feet to groundwater or bedrock in highly permeable soils and in cherty clay soils in areas of severe geological limitations, and a percolation rate slower than sixty minutes per inch pulls a registered engineer onto the design.
The soil evaluation is what settles it for your particular lot.
Source: 19 CSR 20-3.060(5)(A)2., Missouri Code of State Regulations, read 2026-08-26.
Which towns does this cover?
Franklin County has Union as its county seat. Places served include Union, Washington, Pacific, Sullivan, St. Clair, New Haven, Gerald, Berger, Leslie, Gray Summit, Miramiguoa Park, Oak Grove. Anywhere in the county not on a public sewer is on a system this page applies to.
Who is allowed to do the work here?
An installer registered with the Missouri Department of Health and Senior Services. That is a state requirement rather than a county one, and it applies wherever you are. Some counties add their own licensing on top of it, which is one more reason to ask the permitting authority what they require before you sign anything.
How to check an installer's registration takes one phone call.
Source: Section 701.031, Revised Statutes of Missouri, read 2026-08-26.
What we could not confirm for this county
Franklin County publishes no septic or building fee schedule online: its own page says to contact the department for a list of fees, so no figure is stated here. The text of the 2025 ordinance itself was not obtainable online, only its title, adoption date and effective date, so what it requires beyond the state minimum standard is not established here. Ask the Building Department for a copy of the ordinance and the current fees.
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Tell us the county and the jobLast reviewed 2026-08-26.