Lagoon systems: wastewater treatment plants in Illinois
471 plants · 71% of the state · 483 MGD reported by 458 plants
Klarifi identifies 471 publicly owned wastewater treatment plants with lagoon systems in Illinois, 71% of the 664 plants in the state (483 MGD reported by 458 plants). The largest is Metropolitan Water Reclamation in Chicago at 281.73 MGD.
Lagoon systems treat wastewater in large earthen ponds over weeks of retention time, with or without mechanical aeration. They serve thousands of small towns because they are cheap to run, but they struggle with ammonia and nutrient limits, fill with sludge over decades and are the plants most often converted or upgraded when a permit is renewed.
The largest lagoons in Illinois
| # | Facility | City | Avg flow (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| 1 | Metropolitan Water Reclamation | Chicago | 281.73 | ILL028061 | Dec 2030 | 10 |
| 2 | Greater Peoria Sanitary And Sewage District | Peoria | 19.22 | ILL021288 | Dec 2030 | 12 |
| 3 | Spring Creek STP | Springfield | 16.41 | ILL021989 | Dec 2030 | 29 |
| 4 | Glenbard Wastewater Authority | Glen Ellyn | 11.79 | ILL021547 | Dec 2030 | 27 |
| 5 | Collinsville Wastewater Treatment Plant | Collinsville | 11.53 | ILL028215 | Dec 2030 | 5 |
| 6 | Danville Sanitary District STP | Danville | 8.45 | ILL020788 | Dec 2030 | 9 |
| 7 | Frankfort, Village Of | Frankfort | 4.97 | ILL072192 | Dec 2030 | 7 |
| 8 | Bloomington-Normal WRD SE WWTP | Bloomington | 4.04 | ILL073504 | Dec 2030 | 0 |
| 9 | City Of Monmouth | Monmouth | 3.88 | ILL036218 | Dec 2030 | 19 |
| 10 | Moline South Treatment Plant | Moline | 3.64 | ILL029939 | Dec 2030 | 4 |
Plants planning lagoon systems upgrades
These plants report lagoon systems as a planned process in the EPA Clean Watersheds Needs Survey: the earliest public signal of a project.
| Facility | City | Avg flow (MGD) | NPDES permit | Expires |
|---|---|---|---|---|
| Augusta Stp, Village Of | Augusta | 0.04 | IL0027570 | Aug 2027 |
Contacts and project signals for every plant on this list
Klarifi adds verified decision-maker contacts, permit limits, discharge monitoring data and the capital projects planned in each city, filterable by technology, size and compliance record.
Other technologies in Illinois
Lagoon systems in other states
Lagoon systems in Illinois: questions
Sources and methodology
Flow, permit and violation figures come from the EPA's ICIS-NPDES discharge monitoring records. Population served comes from the Clean Watersheds Needs Survey 2022. Treatment structures are identified by Klarifi's review of aerial imagery, and capital improvement projects are extracted from published municipal budget documents. Violations are counted over the last three years of monitoring reports.
Data refreshed October 26, 2026.
Wastewater terms: WWTP · POTW · Biosolids · Filter press · FOG · all terms