ISWS maintains a network of more than 370 monitoring wells to track Illinois’ groundwater levels. These wells are categorized by geologic unit and distributed across the state’s major aquifers. Our staff measure these wells via real-time telemetry systems or periodic site visits.
Browse some of our major groundwater monitoring networks below. You can also click any well link to view its hydrograph and download data.
Prefer a visual view? Use our interactive Illinois Groundwater Monitoring Network map to explore well locations and data geographically.
City of Decatur
The City of Decatur maintains a groundwater monitoring well network in southeastern DeWitt, northeastern Macon, and western Piatt counties to monitor groundwater levels in the Mahomet aquifer and overlying Glasford aquifer. This monitoring well network was established in 1989 during the construction of Decatur’s emergency supply well field. The purpose of the network is to monitor water levels during emergencies when the City of Decatur uses the well field, but it also serves as a valuable record of seasonal and long-term changes in the Mahomet aquifer.
Since 2020, ISWS has partnered with the City of Decatur to measure water levels at select monitoring wells in near real time, on an hourly basis. Tracking water levels long-term provides valuable information on aquifer conditions and whether current demands on the aquifer are outpacing recharge to the system. This information will be important as the aquifer becomes relied upon more for domestic, municipal, and irrigation use.
Monitoring Wells
The following wells are equipped with real-time data or are measured periodically. Click on a well to view the hydrograph and download associated data. All wells are open to the Mahomet aquifer unless noted.
Real-Time Monitoring Wells
Periodic Monitoring Wells
Deep Sandstone
In partnership with the Illinois Department of Natural Resources through the Office of Water Resources, ISWS maintains a long-term groundwater monitoring well network of deep sandstone wells in northeastern Illinois.
The wells are open to the Cambrian-Ordovician sandstone aquifer system, which consists of the St. Peter, Ironton-Galesville, and Mt. Simon sandstone units. The monitoring wells are a mix of dedicated observation wells, abandoned municipal production wells, and production wells that are active only in emergencies. The purpose of this network is to monitor the deep sandstone aquifers around the Chicago metropolitan area in response to inner and northern suburban communities switching to Lake Michigan water and to continued withdrawals by western and southwestern suburban communities, thereby aiding long-term water supply planning in the region.
Real-Time Monitoring Wells
- Des Plaines 7
- Elwood 7
- Fermilab 4
- Fox Metro 2
- Geneva 5
- Hickory Hills 2
- Joliet 23
- Joliet 27
- Joliet 29
- Joliet Corrections 3
- Lake Barrington Shores 2
- Metropolitan Sanitary District (Calumet Plant)
- Newark 1 (Ironton-Galesville)
- Newark 2 (St. Peter)
- Orland Park 11
- Villa Park 7
- Zion 1 (St. Peter)
- Zion 3 (Upper Mt. Simon)
- Zion 4 (Lower Mt. Simon)
Green River Lowlands
The Green River Lowlands in Lee, Whiteside, and Bureau counties is a heavily irrigated portion of Illinois, comprised of the uppermost Tampico Aquifer and the lowermost Sankoty Aquifer. These aquifers are separated by a clay layer that becomes more extensive to the south of the Rock River. For more details on the region’s hydrogeology, see ISWS Data/Case Study 2004-01.
Irrigation is predominantly in the deeper Sankoty Aquifer, which experienced its largest observed drawdown during the 2012 drought in northwestern Bureau County. ISWS currently operates nine real-time monitoring stations in the region — supplemented by periodic hand-measurements at multiple other wells — to track the impact of irrigation and the potential for groundwater flooding during rainy seasons.
The Green River Lowlands network is funded by the Illinois Department of Natural Resources Office of Water Resources as part of water supply planning.
Real-Time Monitoring Wells
Tampico
Sankoty
Imperial Valley
For over 30 years, ISWS has operated a network of rain gages and groundwater observation wells in Mason and Tazewell counties for the Imperial Valley Water Authority. Learn more about our Imperial Valley precipitation and groundwater monitoring and access real-time groundwater data.
Kane County
Groundwater is the primary water source for Kane County’s communities and homeowners. However, as suburbs expand westward from Chicago and communities grow, demands on regional aquifers may increase over the coming decades.
To help manage groundwater resources, ISWS partnered with the Sugar Grove Water Authority in 2017 to establish a monitoring well network in Sugar Grove Township, Kane County. This network monitors groundwater conditions in the shallow sand and gravel aquifer and the shallow bedrock (Silurian Dolomite) aquifer systems. Read our report on recent trends in Sugar Grove Township’s groundwater.
Building on that foundation, Kane County funded a countywide expansion of the Sugar Grove monitoring network in 2023. Scheduled for full completion by the end of 2026, this expanded network will track water levels across the county’s major sand and gravel and shallow bedrock aquifers (specifically the Silurian Dolomite and Galena-Platteville dolomites). Ultimately, these wells will serve as critical data points for collecting water quality samples, assessing seasonal and long-term trends, and guiding long-term water supply planning.
Real-Time Monitoring Wells
Sugar Grove Township
Additional Kane County Sites
Eastern Mahomet Aquifer
With funding provided by Illinois American Water–Champaign, ISWS monitors water levels at a network of observation wells in the eastern Mahomet aquifer and overlying Glasford aquifer. Many of these sites are nested, meaning Mahomet and Glasford wells are located at the same location, allowing vertical gradients to be established.
The ISWS initiated monitoring water levels in the Mahomet aquifer just west of Champaign in 1953 to help resolve a dispute between the petro-chemical company in Tuscola and the water utility serving Champaign and Urbana. In the 1990s, interest in understanding groundwater flow prompted state funding of the Aquifer Assessment Program, leading to the development of an observation well network in the Mahomet Aquifer of east-central Illinois, as detailed in ISWS Data/Case Study 2008-01. This monitoring network was greatly expanded in 2007-2009 — particularly in Champaign County — with funding from Illinois American Water–Champaign.
The purpose of the network is to collect long-term data to study how the aquifer is affected by large groundwater withdrawals for public, industrial, and irrigation uses. This monitoring also helps ISWS scientists determine how the aquifer is recharged, how it interacts with streams, and how it responds to droughts and floods.
Real-Time Monitoring Wells
- CHAM-07-04B (Bondville)
- CHAM-07-01A (Zahnd Pond) – Mahomet
- CHAM-07-01C (Zahnd Pond) – Glasford
- CHAM-08-02A (Middle Fork FP East) – Mahomet
- CHAM-08-02B (Middle Fork FP East) – Glasford
- CHAM-08-03A (S of Ludlow) – Mahomet
- CHAM-08-03B (S of Ludlow)- Glasford
- CHAM-08-08A (Lake of the Woods FP) – Mahomet
- CHAM-08-08B (Lake of the Woods FP) – Glasford
- CHAM-08-09A (Sangamon River) – Mahomet
- CHM-95B (North Mattis) – Mahomet
- CHAM-08-06 (North Mattis) – Glasford
- CHAM-09-03A (Orr Farms) – Mahomet
- CHAM-09-03C (Orr Farms) – Henry/Glasford
- CHAM-09-05A (Stanton Township Garage)
- CHAM-12-02A (Dillsburg) – Mahomet
- CHAM-12-02C (Dillsburg) – Glasford
- CHAM-20-01 (Dewey New Site)
- CHM-96A (Dewey Old Site)
- CHM-95D (Seymour)
- CHM-96C (County Line)
- IRO-98C (Crescent City)
- PIA-2000A (Cisco)
- PIAT-09-01A (Railroad Museum) – Mahomet
- PIAT-09-01B (Railroad Museum) – Glasford
- Petro North
- Petro South
- VERM-08-01A (Armstrong)
Publications
Read relevant monitoring and modeling reports related to the eastern Mahomet aquifer.
- Anomalous groundwater pressure responses in the Mahomet Aquifer near the Manlove Gas Storage Field
- Status of Water Levels in the Mahomet Aquifer near Champaign-Urbana: 2009-2014
- Meeting East-Central Illinois Water Needs to 2050: Potential Impacts on the Mahomet Aquifer and Surface Reservoirs
- The 2012 Drought in Illinois
McLean & Tazewell Counties
ISWS, under contract to the twin municipalities of Bloomington and Normal, has monitored and maintained a groundwater observation well network in McLean and Tazewell counties since 1993. The network was installed as part of a large aquifer assessment and modeling project described in Cooperative Groundwater Report 19.
Real-Time Monitoring Wells
Data at sites marked with an asterisk are still undergoing QA/QC.
Publications
Each year, ISWS submits a letter report to the Mayor of Normal, as well as to other interested sponsors and groups in the area. The letter contains hydrographs for each well, a summary of the information gathered to date, and an analysis of the data where warranted by the findings.
Northern Logan County
ISWS, under contract to the Northern Logan County Water Authority, continuously monitors five wells in northern Logan County.
Real-Time Monitoring Wells
Two water levels are monitored at MTH-22: deep (D) and shallow (S). These four wells are part of the larger McLean and Tazewell counties monitoring network. Data at MTH-22S are still undergoing QA/QC.
Publications
ISWS submits an annual letter report to sponsors and interested groups in the area. The letter contains hydrographs for each well, a summary of the information gathered to date, and some data analysis where findings warrant it.
Shallow Groundwater Wells Network
The Shallow Groundwater Wells Network consists of two groups of wells: Water and Atmospheric Resources Monitoring (WARM) wells and Illinois Climate Network (ICN) wells. The WARM wells are visited monthly, and water level data are recorded on a paper chart using a Stevens Type-F recorder. Currently, only the month-end hand measurements are recorded digitally. The ICN wells are visited less often and on an irregular basis, with hourly, digitally recorded measurements downloaded.
Learn more about our Shallow Groundwater Wells Network and access its groundwater data.