Lagoon systems: wastewater treatment plants in Illinois
481 plants · 75% of the state · 141 MGD reported by 389 plants
Klarifi identifies 481 publicly owned wastewater treatment plants with lagoon systems in Illinois, 75% of the 641 plants in the state (141 MGD reported by 389 plants). The largest is Bloomington Normal WRD -West STP in Bloomington at 10.71 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 | Bloomington Normal WRD -West STP | Bloomington | 10.71 | ILL027731 | Dec 2030 | 0 |
| 2 | Spring Creek STP | Springfield | 7.59 | ILL021989 | Dec 2030 | 28 |
| 3 | Glenbard Wastewater Authority | Glen Ellyn | 7.04 | ILL021547 | Dec 2030 | 27 |
| 4 | Urbana & Champaign Sd | Urbana | 6.2 | ILL031500 | Dec 2030 | 2 |
| 5 | Danville Sanitary District STP | Danville | 5 | ILL020788 | Dec 2030 | 11 |
| 6 | Wheaton Sanitary District WWTF | Wheaton | 4.5 | ILL031739 | Dec 2030 | 7 |
| 7 | Sterling WWTP | Sterling | 4.31 | IL0060569 | Sep 2024 | 5 |
| 8 | Scwrd Sugar Creek WWTP | Springfield | 3.95 | ILL021971 | Dec 2030 | 9 |
| 9 | Frankfort, Village Of | Frankfort | 3.32 | ILL072192 | Dec 2030 | 7 |
| 10 | Galesburg Sanitary District STP | Galesburg | 3.22 | ILL023141 | Dec 2030 | 6 |
| 11 | Belleville Wastewater Treatment Facility | Belleville | 3 | ILL021873 | Dec 2030 | 2 |
| 12 | Bloomington-Normal WRD SE WWTP | Bloomington | 2.94 | ILL073504 | Dec 2030 | 0 |
| 13 | Moline South Treatment Plant | Moline | 2.72 | ILL029939 | Dec 2030 | 3 |
| 14 | City Of Monmouth | Monmouth | 2.64 | ILL036218 | Dec 2030 | 20 |
| 15 | Collinsville Wastewater Treatment Plant | Collinsville | 2.59 | ILL028215 | Dec 2030 | 5 |
| 16 | Pekin STP #1 | Pekin | 2.4 | ILL034495 | Dec 2030 | 7 |
| 17 | City Of East Peoria Wastwater Treatment Plant | East Peoria | 2.25 | ILL028576 | Dec 2030 | 6 |
| 18 | Jacksonville STP | Jacksonville | 2.16 | ILL021661 | Dec 2030 | 1 |
| 19 | Rochelle City Of | Rochelle | 2.12 | ILL030741 | Dec 2030 | 0 |
| 20 | Morton STP 2 | Morton | 2.11 | ILL030015 | Dec 2030 | 222 |
| 21 | Woodstock Northside Wastewater Treatment Plant | Woodstock | 1.77 | ILL031861 | Dec 2030 | 3 |
| 22 | Kewanee STP | Kewanee | 1.71 | IL0029343 | Apr 2031 | 37 |
| 23 | Christian County Water Reclamation District | Taylorville | 1.58 | IL0031356 | Jul 2031 | 0 |
| 24 | Streator STP | Streator | 1.37 | ILL022004 | Dec 2030 | 31 |
| 25 | Washington STP #2 | Washington | 1.13 | IL0042412 | Oct 2030 | 0 |
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 | — | 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 September 11, 2026.