Coffeen Lake Dam
Coffeen Lake Dam is an earth dam located in Montgomery County, Illinois, built in 1964. It carries a Significant hazard potential classification.
About Coffeen Lake Dam
Coffeen Lake Dam is a dam in Montgomery, Illinois. The dam is owned by Dynegy Midwest Generation, Inc. (public utility). It impounds the Mc David Branch, Shoal Creek near Greenville.
The dam stands 70 feet tall and stretches 1,300 feet across, creates a reservoir covering 1,096 acres, has a maximum storage capacity of 35,800 acre-feet, and collects water from a drainage area of 19 square miles. Completed in 1964, the structure is well into its service life at over 50 years old.
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 09/17/2025.
At 70 feet, this dam is taller than 96% of all dams in the United States.
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Location
| State | Illinois |
| County | Montgomery |
| Nearest City | Greenville |
| River/Stream | Mc David Branch, Shoal Creek |
| Coordinates | 39.03516, -89.38671 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 70 ft |
| Dam Height | 70 ft |
| Dam Length | 1,300 ft |
| Year Completed | 1964 (62 years old) |
Storage & Hydraulics
| NID Storage | 35,800 acre-ft |
| Max Storage | 35,800 acre-ft |
| Normal Storage | 22,000 acre-ft |
| Surface Area | 1,096 acres |
| Drainage Area | 19 sq mi |
| Max Discharge | 8,430 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Other |
| Owner | DYNEGY MIDWEST GENERATION, INC. |
| Owner Type | Public Utility |
| Hazard Classification | Significant |
| Condition Assessment | Not Available |
| Last Inspection | 09/17/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL00135 |
| Federal ID | IL00135 |
| More Info | State Dam Safety Program |