Septic Systems in Illinois

Septic Systems in Illinois

Approximately 12% of homes in Illinois rely on septic systems for wastewater treatment, totaling an estimated 284,804 septic systems across the state's 102 counties. This places Illinois among the states with significant decentralized wastewater infrastructure.

Septic Regulations in Illinois

Septic regulations in Illinois are administered by Illinois Department of Health/Environment, with permits typically issued at the county level through local health departments. Requirements for tank sizes, setback distances, approved system types, and inspections can vary significantly between counties.

While Illinois does not have a statewide mandate for septic inspections at the time of property sale, individual counties may impose their own requirements. It is common practice for buyers to request a septic inspection as part of their due diligence, even when not legally required.

Common Septic System Types

Homeowners in Illinois typically use one of several septic system types depending on local soil conditions: conventional gravity-fed systems where soil percolation is adequate, pressure distribution systems in areas with moderate limitations, mound systems where shallow bedrock or high water tables prevent conventional installation, and aerobic treatment units (ATUs) in environmentally sensitive areas.

Septic Maintenance Requirements

The EPA recommends pumping septic tanks every 3 to 5 years, though the exact frequency depends on tank size, household size, and water usage. In Illinois, some counties have adopted mandatory pumping schedules or maintenance tracking programs. Proper maintenance prevents costly repairs, protects groundwater quality, and extends the lifespan of the drainfield — the most expensive component to replace.

Select a county above to view detailed septic regulations, estimated costs, soil suitability data sourced from the USDA NRCS Soil Survey, and groundwater depth measurements from the USGS.