The Thornton Reservoir in Illinois was completed in 2015 and occupies the northern section of Thornton Quarry, providing service to Chicago’s Far South Side and 13 surrounding suburbs, according to the Metropolitan Water Reclamation District of Greater Chicago (MWRD). The project was established under the Tunnel and Reservoir Plan (TARP), also known as the Deep Tunnel, to collect excess stormwater and sewage before it could spill into rivers during heavy rainfall. After heavy storms in July 2026, it reached 94% of its 7.9-billion-gallon capacity and captured more than 7.3 billion gallons of water. Its capacity was expanded from an original 14,600 acre-feet to 24,200 acre-feet, per the US Army Corps of Engineers.
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