Prairie Grass Boulevard Dam is an earth dam located in Will County, Illinois. It carries a Significant hazard potential classification.
Dam profile
NID height · 6 ft6 ft tall and 750 ft long. Height is drawn to scale against a two-story house, about 25 ft; the profile is a generic embankment section and the water level is illustrative.
About Prairie Grass Boulevard Dam
The primary purpose of Prairie Grass Boulevard 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 Whispering Prairie Inc. (private). It impounds the Trib Forked Creek near Wilmington.
The dam stands 6 feet tall and stretches 750 feet across, has a maximum storage capacity of 27 acre-feet, and collects water from a drainage area of 1 square miles.
This dam has a significant hazard potential classification, meaning that a failure could cause significant economic damage — flooding roads, bridges, or property downstream — but is not expected to result in loss of life. An emergency action plan is in place for this dam. The most recent inspection on record was 05/07/2025.
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Location
| State | Illinois |
| County | Will |
| Nearest City | Wilmington |
| River/Stream | Trib Forked Creek |
| Coordinates | 41.39246, -87.85555 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 6 ft |
| Dam Height | 6 ft |
| Dam Length | 750 ft |
Storage & Hydraulics
| NID Storage | 27 acre-ft |
| Max Storage | 27 acre-ft |
| Drainage Area | 1 sq mi |
| Max Discharge | 938 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Flood Risk Reduction |
| Owner | Whispering Prairie Inc. |
| Owner Type | Private |
| Hazard Classification | Significant |
| Condition Assessment | Not assessed |
| Last Inspection | 05/07/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL55095 |
| Federal ID | IL55095 |
| More Info | State Dam Safety Program |