Thorton Quarry Gap Dam
Thorton Quarry Gap Dam is a concrete dam located in Cook County, Illinois, built in 2013. It carries a High hazard potential classification.
About Thorton Quarry Gap Dam
The primary purpose of Thorton Quarry Gap Dam is flood risk reduction. The dam is designed to control downstream flooding by temporarily storing excess water during storms and releasing it at a controlled rate. The dam is owned by Metropolitan Water Reclamation District (private). It impounds the Thornton Quarry near Thornton.
The dam stands 116 feet tall and stretches 220 feet across, has a maximum storage capacity of 9,900 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 2013, the structure is relatively new.
This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. An emergency action plan is in place for this dam. The most recent inspection on record was 05/13/2025.
At 116 feet, this dam is taller than 98% of all dams in the United States.
Living Downstream
If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Illinois dam safety program can provide more specific information about emergency planning for this structure.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | Illinois |
| County | Cook |
| Nearest City | Thornton |
| River/Stream | Thornton Quarry |
| Coordinates | 41.57987, -87.61897 |
Physical Characteristics
| Dam Type | Concrete |
| NID Height | 116 ft |
| Dam Height | 116 ft |
| Dam Length | 220 ft |
| Year Completed | 2013 (13 years old) |
Storage & Hydraulics
| NID Storage | 9,900 acre-ft |
| Max Storage | 9,900 acre-ft |
| Drainage Area | 0 sq mi |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Flood Risk Reduction |
| Owner | METROPOLITAN WATER RECLAMATION DISTRICT |
| Owner Type | Private |
| Hazard Classification | High |
| Condition Assessment | Not Available |
| Last Inspection | 05/13/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL55136 |
| Federal ID | IL55136 |
| More Info | State Dam Safety Program |