← Septic cost calculator · All 50 states
A conventional gravity system for a 3-bedroom house on average soil runs about $4,700 – $9,500 installed in Illinois — roughly 18% above the national baseline. Illinois ranks 49 of 51 for construction labor cost, pricier than most states.
3-bedroom house, average soil, Illinois labor market.
| System type | Estimated installed cost |
|---|---|
| Conventional Gravity | $4,700 – $9,500 |
| Aerobic Treatment Unit (ATU) | $11,800 – $23,700 |
| Mound / Sand-Filter System | $11,800 – $23,700 |
Conventional gravity system, average soil.
| Bedrooms | Estimated installed cost |
|---|---|
| 1–2 bedrooms (750-gal tank) | $4,000 – $8,000 |
| 3 bedrooms (1,000-gal tank) | $4,700 – $9,500 |
| 4 bedrooms (1,250-gal tank) | $5,400 – $10,900 |
| 5+ bedrooms (1,500-gal tank) | $6,400 – $12,800 |
Roughly half a septic install is labor and machine time. We take that share and scale it by what the two trades that actually do the work earn in Illinois, against the national mean — U.S. Bureau of Labor Statistics, Occupational Employment and Wage Statistics, May 2025:
| Construction Laborers (SOC 47-2061), Illinois mean | $67,620 |
| Construction Laborers, national mean | $52,030 |
| Construction Equipment Operators (SOC 47-2073), Illinois mean | $90,500 |
| Construction Equipment Operators, national mean | $66,290 |
| Illinois wage level vs national | 133% |
| Applied to the 55% labor share → cost index | 118% |
Tanks, pipe, gravel and freight are priced closer to nationally, so the whole job does not swing as far as wages do. Source: bls.gov/oes.
Illinois's permit fees, county perc-test requirements, setback rules and inspection schedule are set locally, and we do not model them per state — the permits line in the estimate is a national typical. Two counties in Illinois can differ more than Illinois differs from Arkansas. Check with your county health department before you budget, and get a written bid.
Range across all 51: Arkansas 85% → Hawaii 125%. See every state →
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