In Montana, onsite wastewater (septic) systems are regulated by Montana Department of Environmental Quality (DEQ), Water Quality Division — Engineering Infrastructure and Subdivisions Program, which sets the statewide code, and permits are issued and inspections carried out by county or local health jurisdictions. Installing, replacing or repairing a septic system here means, in sequence: a site and soil evaluation, a design, a permit application, an inspection while the system is open, and a final as-built record once it is approved.
The state-level regulator is Montana Department of Environmental Quality (DEQ), Water Quality Division — Engineering Infrastructure and Subdivisions Program (official program page). DEQ sets statewide design and siting standards and reviews new subdivisions for sanitation adequacy under the Sanitation in Subdivisions Act, issuing a Certificate of Subdivision Approval. Septic permits for individual non-subdivision lots, construction and drainfield permits, inspections, and installer licensing are issued and enforced locally by county or city-county health department sanitarians under DEQ rules.
The statewide onsite-wastewater code is cited as Administrative Rules of Montana (ARM) Title 17, chapter 36 (subsurface/onsite wastewater treatment systems, implementing the Sanitation in Subdivisions Act), with design standards in Department Circular DEQ-4 ("Montana Standards for Subsurface Wastewater Treatment Systems"). We link the agency's own page above rather than restating specific numeric requirements from it, since those change by rule revision and by local amendment.
The order of operations is broadly consistent across the country, even though the specific numbers in each step vary by state and often by county. None of the figures below are specific to Montana; treat this as the shape of the process, and get the actual numbers from the agency linked above or from the county office.
| Design | A licensed Professional Engineer (registered with the Montana Board of Professional Engineers and Professional Land Surveyors) or a Registered Sanitarian; ARM requires a PE for larger design flows and for experimental systems, and most county programs require the site evaluation/design be prepared or approved by a PE or Registered Sanitarian. https://deq.mt.gov/water/Programs/eng |
|---|---|
| Installation | No single statewide DEQ installer license for constructing septic systems — installer licensing/certification is administered county by county (for example Missoula City-County Health Department issues a Septic System Installer certification and Lincoln County issues its own Installer License), generally without reciprocity. Separately, DEQ statewide licenses "Septic Tank Pumpers" for pumping/cleaning and septage disposal, a distinct license from new-system installation. https://deq.mt.gov/twr/Programs/septic-tank |
Septic records in Montana are generally held by the county or local health jurisdiction that issued the permit, not by the state agency, and are released under the state's public records law. We have not logged the specific statute name and response deadline for Montana yet; check with the county office listed on its records page below, or with Montana Department of Environmental Quality (DEQ), Water Quality Division — Engineering Infrastructure and Subdivisions Program.
We hold 14,658 septic records across 20 of 56 Montana counties. Each county page below shows exactly where its records are kept and how many we hold.
| County | Records held |
|---|---|
| Flathead | 13,209 |
| Lincoln | 998 |
| Park | 256 |
| Yellowstone | 82 |
| Carbon | 26 |
| Jefferson | 13 |
| Lake | 12 |
| Toole | 11 |
| Sweet Grass | 8 |
| Teton | 7 |
| Silver Bow | 6 |
| Pondera | 6 |
| Madison | 6 |
| Deer Lodge | 5 |
| Ravalli | 5 |
| Cascade | 4 |
| Broadwater | 1 |
| Rosebud | 1 |
| Fergus | 1 |
| Stillwater | 1 |
Full Montana county-by-county index · Open the parcel map
Montana Department of Environmental Quality (DEQ), Water Quality Division — Engineering Infrastructure and Subdivisions Program. DEQ sets statewide design and siting standards and reviews new subdivisions for sanitation adequacy under the Sanitation in Subdivisions Act, issuing a Certificate of Subdivision Approval. Septic permits for individual non-subdivision lots, construction and drainfield permits, inspections, and installer licensing are issued and enforced locally by county or city-county health department sanitarians under DEQ rules.
The sequence is a site and soil evaluation, a design sized from the evaluation and (under most state codes) bedroom count, a permit application, an inspection before backfill, and a final as-built filed once the system is approved. Exact numeric requirements are set by the agency's own code, not restated here.
No single statewide DEQ installer license for constructing septic systems — installer licensing/certification is administered county by county (for example Missoula City-County Health Department issues a Septic System Installer certification and Lincoln County issues its own Installer License), generally without reciprocity. Separately, DEQ statewide licenses "Septic Tank Pumpers" for pumping/cleaning and septage disposal, a distinct license from new-system installation. https://deq.mt.gov/twr/Programs/septic-tank
Septic records are generally held by the county or district health office that issued the permit. See our county-by-county Montana index for the specific office and portal in each county.
Regulatory information on this page was researched against official state agency sources and last verified 2026-08-31. It is informational only: the agency linked above is authoritative, and requirements can change. We are not lawyers, not a government body, and not affiliated with, licensed or certified by any agency named on this page.