Lake of Egypt Dam is an earth dam located in Williamson County, Illinois, built in 1962. It carries a High hazard potential classification.
Dam profile
NID height · 55 ft55 ft tall and 2,850 ft long, taller than 94% of U.S. dams with a recorded height. Height is drawn to scale against a ten-story building, about 100 ft; the profile is a generic embankment section and the water level is illustrative.
About Lake of Egypt Dam
Lake of Egypt Dam is a dam in Williamson, Illinois. The dam is owned by Southern Illinois Power Cooperative (public utility). It impounds the South Fork Saline River near Marion-offstream.
The dam stands 55 feet tall and stretches 2,850 feet across, creates a reservoir covering 2,265 acres, has a maximum storage capacity of 82,942 acre-feet, and collects water from a drainage area of 33 square miles. Completed in 1962, the structure is well into its service life at over 50 years old.
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 11/11/2025.
At 55 feet, this dam is taller than 94% of dams nationwide.
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 | Williamson |
| Nearest City | Marion-offstream |
| River/Stream | South Fork Saline River |
| Coordinates | 37.62326, -88.94671 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 55 ft |
| Dam Height | 55 ft |
| Dam Length | 2,850 ft |
| Year Completed | 1962 (64 years old) |
Storage & Hydraulics
| NID Storage | 82,942 acre-ft |
| Max Storage | 82,942 acre-ft |
| Normal Storage | 41,215 acre-ft |
| Surface Area | 2,265 acres |
| Drainage Area | 33 sq mi |
| Max Discharge | 40,666 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Other |
| Owner | Southern Illinois Power Cooperative |
| Owner Type | Public Utility |
| Hazard Classification | High |
| Condition Assessment | Not assessed |
| Last Inspection | 11/11/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL00015 |
| Federal ID | IL00015 |
| More Info | State Dam Safety Program |