Lake Mattoon Dam
Lake Mattoon Dam is an earth dam located in Shelby County, Illinois, built in 1957. It carries a Significant hazard potential classification.
About Lake Mattoon Dam
The primary purpose of Lake Mattoon Dam is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by City Of Mattoon (local government). It impounds the Little Wabash River near Effingham.
The dam stands 46 feet tall and stretches 2,250 feet across, creates a reservoir covering 980 acres, has a maximum storage capacity of 22,569 acre-feet, and collects water from a drainage area of 57 square miles. Completed in 1957, 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 12/09/2025.
At 46 feet, this dam is taller than 91% of dams nationwide.
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Location
| State | Illinois |
| County | Shelby |
| Nearest City | Effingham |
| River/Stream | Little Wabash River |
| Coordinates | 39.33331, -88.48173 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 46 ft |
| Dam Height | 46 ft |
| Dam Length | 2,250 ft |
| Year Completed | 1957 (69 years old) |
Storage & Hydraulics
| NID Storage | 22,569 acre-ft |
| Max Storage | 22,569 acre-ft |
| Normal Storage | 11,820 acre-ft |
| Surface Area | 980 acres |
| Drainage Area | 57 sq mi |
| Max Discharge | 28,273 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Recreation |
| Owner | CITY OF MATTOON |
| Owner Type | Local Government |
| Hazard Classification | Significant |
| Condition Assessment | Not Available |
| Last Inspection | 12/09/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL00141 |
| Federal ID | IL00141 |
| More Info | State Dam Safety Program |