How many wastewater treatment plants are there in Illinois?

Klarifi tracks 638 publicly owned wastewater treatment plants in Illinois with a combined average flow of 664 million gallons per day, serving about 5,800,878 residents. 65 of them treat more than 1 MGD and 6 more than 10 MGD.

What is the largest wastewater treatment plant in Illinois?

MWRDGC Terrence J O'Brien Water Reclamation Plant in Skokie is the largest plant in Illinois by average flow, treating about 170 MGD.

What treatment technologies are common in Illinois?

477 of Illinois's plants use lagoon systems and 92 have biogas or anaerobic digestion infrastructure, based on Klarifi's aerial imagery review.

How many NPDES permits in Illinois are up for renewal?

21 permits held by Illinois plants expire in 2026 and 293 in 2027. Renewals typically bring new limits and trigger upgrade projects.

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Wastewater treatment plants in Illinois

Name: Wastewater treatment plants in Illinois
Creator: Klarifi
License: https://klarifi.io/terms-of-service

638 facilities · 664 MGD combined flow

Klarifi tracks 638 publicly owned wastewater treatment plants in Illinois with a combined average flow of 664 MGD, serving about 5,800,878 residents. 65 plants treat more than 1 MGD and 6 more than 10 MGD; 477 use lagoon systems and 92 have digesters or biogas infrastructure. The largest is MWRDGC Terrence J O'Brien Water Reclamation Plant in Skokie at 170 MGD. 21 NPDES permits expire this year and 293 next year.

Every plant below links to a profile with average and design flow, the NPDES permit and its expiry, a three-year compliance snapshot and the capital projects planned in its city. Treatment technology and verified contacts are shown with a free Klarifi account. Showing facilities 1–200 of 638 by average flow — browse the rest with the page links below.

638 plant locations in Illinois; dot size follows average flow.

NPDES permits and renewals in Illinois

Every plant discharges under an NPDES permit that is renewed every five years, usually with tighter limits. The renewal year is the year a plant budgets for upgrades.

All NPDES permits in Illinois →21 permits expiring in 2026 →293 permits expiring in 2027 →64 permits expiring in 2028 →Find plants near you on the map →

Largest wastewater treatment plants in Illinois

The 10 largest publicly owned wastewater treatment plants in Illinois by average flow, with NPDES permit, expiry and three-year violation count. Source: EPA ICIS-NPDES via Klarifi.
Facility	City	Avg flow (MGD)	Design (MGD)	NPDES permit	Expires	Violations (3y)
MWRDGC Terrence J O'Brien Water Reclamation Plant	Skokie	170	450	IL0028088	Jul 2022	18
Metropolitan Water Reclamation	Chicago	155	—	ILL028061	Dec 2030	11
Sanitary District Of Decatur	Decatur	26.53	—	ILL028321	Dec 2030	1
Springbrook Water Reclamation Center	Naperville	17.26	—	ILL034061	Dec 2030	0
Greater Peoria Sanitary And Sewage District	Peoria	13.17	—	ILL021288	Dec 2030	10
Bloomington Normal WRD -West STP	Bloomington	10.71	—	ILL027731	Dec 2030	0
Fox River Water Reclamation Dist	Elgin	10	—	ILL028657	Dec 2030	51
Flagg Creek Water Reclamation	Burr Ridge	8.31	—	ILL022586	Dec 2030	5
Elmhurst Stp, City Of	Elmhurst	7.92	—	ILL028746	Dec 2030	8
Lake County Public Works Department	Buffalo Grove	7.89	—	ILL022055	Dec 2030	1

Treatment technology for each plant is shown with a free Klarifi account. Create one →

The 50 largest plants in Illinois →EPA enforcement actions in Illinois →Illinois capital improvement plans →

Illinois plants by treatment technology

Lagoon systems (477)Activated sludge and clarifiers (158)Anaerobic digesters and biogas (92)Oxidation ditches (56)

All 638 plants in Illinois

Facility	City	Flow (MGD)
MWRDGC Terrence J O'Brien Water Reclamation Plant	Skokie	170
Metropolitan Water Reclamation	Chicago	155
Sanitary District Of Decatur	Decatur	26.53
Springbrook Water Reclamation Center	Naperville	17.26
Greater Peoria Sanitary And Sewage District	Peoria	13.17
Bloomington Normal WRD -West STP	Bloomington	10.71
Fox River Water Reclamation Dist	Elgin	10
Flagg Creek Water Reclamation	Burr Ridge	8.31
Elmhurst Stp, City Of	Elmhurst	7.92
Lake County Public Works Department	Buffalo Grove	7.89
Spring Creek STP	Springfield	7.59
Glenbard Wastewater Authority	Glen Ellyn	7.04
Joliet West Stp, City Of	Joliet	6.67
Downers Grove Sanitary District	Downers Grove	6.39
Urbana & Champaign Sd	Urbana	6.2
Woodridge-Greene Valley WWTP	Woodridge	6.1
Alton Waste Water Treatment Plant	Alton	5.38
Danville Sanitary District STP	Danville	5
Romeoville Wastewater Treatment Facility	Romeoville	4.81
Wheaton Sanitary District WWTF	Wheaton	4.5
Plainfield North Stp, Village Of	Plainfield	4.34
Sterling WWTP	Sterling	4.31
Scwrd Sugar Creek WWTP	Springfield	3.95
East Moline Wastewater	East Moline	3.74
North Slope Treatment Plant	Moline	3.43
Frankfort, Village Of	Frankfort	3.32
Galesburg Sanitary District STP	Galesburg	3.22
Fox River Water Reclamation Di	Elgin	3.21
Bloomington-Normal WRD SE WWTP	Bloomington	2.94
Moline South Treatment Plant	Moline	2.72
City Of Monmouth	Monmouth	2.64
Collinsville Wastewater Treatment Plant	Collinsville	2.59
Village Of Bolingbrook STP #3	Bolingbrook	2.52
Pekin STP #1	Pekin	2.4
Edwardsville Stp, City Of	Edwardsville	2.3
Algonquin Stw, Village Of	Algonquin	2.3
Sycamore STP - North Plant	Sycamore	2.26
City Of East Peoria Wastwater Treatment Plant	East Peoria	2.25
Addison Stw North 3	Addison	2.24
Lake In The Hills Sd	Lake In The Hills	2.19
Jacksonville STP	Jacksonville	2.16
Rochelle City Of	Rochelle	2.12
Morton STP 2	Morton	2.11
Metropolitan Water Reclamation District	Lemont	2
Yorkville-Bristol Sd STP	Yorkville	1.99
O Fallon STP	O Fallon	1.98
Marion SE Stp, City Of	Marion	1.96
Village Of Mokena Stw	Mokena	1.84
Deerfield WRF	Deerfield	1.78
Woodstock Northside Wastewater Treatment Plant	Woodstock	1.77
Caseyville Township East STP	O Fallon	1.75
Kewanee STP	Kewanee	1.71
Bartlett Stp, Village Of	Bartlett	1.7
Christian County Water Reclamation District	Taylorville	1.58
New Lenox STP #1, Village Of	New Lenox	1.46
Cary Wwtp, Village Of	Cary	1.38
Effingham STP	Effingham	1.34
A.J. Larocca Wastewater Treatment Facility	Addison	1.22
Washington STP #2	Washington	1.13
Centralia Stw Main, City Of	Centralia	1.12
Harrisburg STP	Harrisburg	1.1
Woodstock South Stp, City Of	Woodstock	1.07
Bolingbrook STP #1	Bolingbrook	1.03
Wood Dale North And South STP	Wood Dale	1.03
Swansea Stp, Village Of	Swansea	1
Robinson Wwtp, City Of	Robinson	0.97
Itasca, Village Of - Prospect Avenue WWTP	Itasca	0.9
Pana STP	Pana	0.9
Manteno Stw, Village Of	Manteno	0.89
Olney Stp, City Of	Olney	0.87
Murphysboro Stp, City Of	Murphysboro	0.85
New Lenox-STP #2, Village Of	New Lenox	0.84
Illinois American Water - Jerseyville STP	Jerseyville	0.83
Huntley East Wwtp, Village Of	Huntley	0.82
Spring Valley WWTP	Spring Valley	0.82
Harvard Wwtp, City Of	Harvard	0.81
East Dundee Wwtp, Village Of	East Dundee	0.81
Manhattan Stw, Village Of	Manhattan	0.81
Coal City Stp, Village Of	Coal City	0.79
Braidwood Stp, City Of	Braidwood	0.77
Morris WWTP #2 - Stp, City Of	Morris	0.73
Elburn Wwtp, Village Of	Elburn	0.71
St. Clair Township Lincolnshire STP	Belleville	0.71
West Frankfort Stw, City Of	West Frankfort	0.7
Plano Stp, City Of	Plano	0.69
Huntley - West WWTP	Huntley	0.69
Salem Stp, City Of	Salem	0.69
Peru STP #2	Peru	0.68
City Of Waterloo STP 3	Waterloo	0.67
Mendota Stp, City Of	Mendota	0.67
Pingree Grove, Village Of	Pingree Grove	0.66
Greenville Stp, City Of	Greenville	0.66
Wilmington Stp, City Of	Wilmington	0.63
Highland Water Reclamation	Highland	0.62
Morton STP 3	Morton	0.62
Illinois American Water-Godfrey Wastewater	Godfrey	0.6
Cerro Gordo Stp, Village Of	Cerro Gordo	0.6
Farmington Sanitary District STP	Farmington	0.58
Roselle-J Botterman STP	Roselle	0.58
Watseka Stw	Watseka	0.58
Beecher Stp, Village Of	Beecher	0.56
Mascoutah, City Of	Mascoutah	0.55
Milan STP	Milan	0.52
Galena South WWTF	Galena	0.52
East Alton Stp, Village Of	East Alton	0.51
Sangamon Valley Pwd STP	Mahomet	0.51
Stookey Township WWTP	Belleville	0.51
Christopher Stp, City Of	Christopher	0.5
Crest Hill West Stp, City Of	Crest Hill	0.47
Anna Stw, City Of	Anna	0.46
Mahomet Stp, Village Of	Mahomet	0.46
Chester STP	Chester	0.46
Georgetown Stp, City Of	Georgetown	0.45
Genoa Stw, City Of	Genoa	0.45
Smithton Stp, Village Of	Smithton	0.45
Fairfield, City Of	Fairfield	0.44
Crystal Lake WWTP #3	Crystal Lake	0.43
Flora Stp, City Of	Flora	0.43
Shelbyville Stw, City Of	Shelbyville	0.43
Johnston City STP	Johnston City	0.42
Duquoin Stp, City Of	Du Quoin	0.42
Fulton Wwtp, City Of	Fulton	0.42
Stockton Stp, Village Of	Stockton	0.41
Auburn Stp, City Of	Auburn	0.41
Leroy Stp, City Of	Le Roy	0.41
Sparta - Southeast Stp, City Of	Sparta	0.41
Eureka WTP	Eureka	0.39
Sigel, Village Of	Sigel	0.38
Caseyville Township West STP	O Fallon	0.38
Illinois American Water - Villa Grove STP	Villa Grove	0.38
Cambridge Stp, Village Of	Cambridge	0.37
St Charles Main Stw East, Stw West	Saint Charles	0.37
Diamond Wwtp, Village Of	Diamond	0.37
Paxton Stp, City Of	Paxton	0.37
Lebanon Stp, City Of	Lebanon	0.37
Geneseo Stp, City Of	Geneseo	0.36
City Of Red Bud	Red Bud	0.36
Elizabeth Stp, Village Of	Elizabeth	0.36
Mount Sterling SE Stp, City Of	Mount Sterling	0.35
Carlyle Stp, City Of	Carlyle	0.35
Pittsfield Stp, City Of	Pittsfield	0.35
Pinckneyville STP 2 East, City Of	Pinckneyville	0.35
Millstadt Stp, Village Of	Millstadt	0.35
Chillicothe Sd	Chillicothe	0.34
Aqua Illinois - Peotone STP	Peotone	0.34
Carterville Stp, City Of	Carterville	0.34
Pinckneyville STP #1	Pinckneyville	0.33
Rockton Stp, Village Of	Rockton	0.33
East Peoria #3 STP	East Peoria	0.32
Elmwood Stp, City Of	Elmwood	0.32
Marissa, Village Of	Marissa	0.31
Breese Stp, City Of	Breese	0.31
Lanark Stp, City Of	Lanark	0.31
Oglesby Stp, City Of	Oglesby	0.31
Rushville Stp, City Of	Rushville	0.31
Tuscola STP	Tuscola	0.31
Carthage Stp, City Of	Carthage	0.3
Orion Wastewater Treatment Plant	Orion	0.3
Amboy Stp, City Of	Amboy	0.3
Carrollton Stp, City Of	Carrollton	0.3
Princeville Stp, Village Of	Princeville	0.3
Sheridan Sanitary District - STP	Sheridan	0.3
Minonk Stw, City Of	Minonk	0.3
Lakewood Stp, Village Of	Lakewood	0.29
Dupo Stp, Village Of	Dupo	0.29
Greenup, Village Of	Greenup	0.29
Oregon Stp, City Of	Oregon	0.29
Henry Stp, City Of	Henry	0.29
Nashville Stp, City Of	Nashville	0.28
Byron Stp, City Of	Byron	0.28
Wbsd Wastewater Treatment Plant	Belgium	0.27
Abingdon Stp, City Of	Abingdon	0.27
Clay City, Village Of	Clay City	0.27
Brighton Stp, Village Of	Brighton	0.26
Colona - Green Rock Regional STP	Colona	0.26
Mason City Stp, City Of	Mason City	0.26
Mt Sterling - Stp, City Of	Mount Sterling	0.26
Neoga Stp, City Of	Neoga	0.26
Equality Stp, Village Of	Equality	0.25
Metamora North Stp, Village Of	Metamora	0.25
Vienna Stp, City Of	Vienna	0.25
Glasford Stp, Village Of	Glasford	0.24
Marengo Stp, City Of	Marengo	0.24
Roanoke Stp, Village Of	Roanoke	0.24
Thomson Stp, Village Of	Thomson	0.24
Poplar Grove South Stp, Village Of	Poplar Grove	0.23
Rend Lake Conservancy District - STP	Ewing	0.23
Polo Stp, City Of	Polo	0.23
Poplar Grove - North Wwtp, Village Of	Poplar Grove	0.22
Davis Junction, Village Of	Davis Junction	0.22
Gilman North Stp, City Of	Gilman	0.22
Casey - Northeast Stp, City Of	Casey	0.21
Marshall Stp, City Of	Marshall	0.21
Ladd Stp, Village Of	Ladd	0.21
Roxana STP	Roxana	0.21
Staunton Stp, City Of	Staunton	0.21
White Hall Stp, City Of	White Hall	0.2
Albion WWTP	Albion	0.2
De Pue	Depue	0.2
Grayville Stp, City Of	Grayville	0.2

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Wastewater treatment 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 14, 2026.

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