Coffeen Gmf Gypsum Stack Dam
Coffeen Gmf Gypsum Stack Dam is an earth dam located in Montgomery County, Illinois. It carries a High hazard potential classification.
About Coffeen Gmf Gypsum Stack Dam
The primary purpose of Coffeen Gmf Gypsum Stack Dam is debris control. The dam is designed to catch sediment, rocks, and debris carried by flowing water — particularly important in areas prone to mudslides or heavy erosion. The dam is owned by Dynegy Midwest Generation, Inc. (public utility). It impounds the Mcdavid Branch East Fork Shoal near Coffeen.
The dam stands 108 feet tall and stretches 5,100 feet across, creates a reservoir covering 38 acres, has a maximum storage capacity of 2,355 acre-feet, and collects water from a drainage area of 38 square miles.
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 09/17/2025.
At 108 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 | Montgomery |
| Nearest City | Coffeen |
| River/Stream | Mcdavid Branch East Fork Shoal |
| Coordinates | 39.07141, -89.39868 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 108 ft |
| Dam Height | 108 ft |
| Dam Length | 5,100 ft |
Storage & Hydraulics
| NID Storage | 2,355 acre-ft |
| Max Storage | 2,355 acre-ft |
| Surface Area | 38 acres |
| Drainage Area | 38 sq mi |
| Max Discharge | 1,100 cfs |
| Spillway Type | Controlled |
Ownership & Safety
| Purpose | Debris Control |
| Owner | DYNEGY MIDWEST GENERATION, INC. |
| Owner Type | Public Utility |
| Hazard Classification | High |
| Condition Assessment | Not Available |
| Last Inspection | 09/17/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL50579 |
| Federal ID | IL50579 |
| More Info | State Dam Safety Program |