Lake Petersburg Dam
Lake Petersburg Dam is an earth dam located in Menard County, Illinois, built in 1961. It carries a High hazard potential classification.
About Lake Petersburg Dam
The primary purpose of Lake Petersburg Dam is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Lake Petersburg Association (private). It impounds the Trib Sangamon River near Petersburg.
The dam stands 85 feet tall and stretches 1,300 feet across, and has a maximum storage capacity of 6,703 acre-feet. Completed in 1961, 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 03/20/2025.
At 85 feet, this dam is taller than 97% 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 | Menard |
| Nearest City | Petersburg |
| River/Stream | Trib Sangamon River |
| Coordinates | 39.98943, -89.84794 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 85 ft |
| Dam Height | 85 ft |
| Dam Length | 1,300 ft |
| Year Completed | 1961 (65 years old) |
Storage & Hydraulics
| NID Storage | 6,703 acre-ft |
| Max Storage | 6,703 acre-ft |
| Normal Storage | 4,303 acre-ft |
| Max Discharge | 1,985 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Recreation |
| Owner | LAKE PETERSBURG ASSOCIATION |
| Owner Type | Private |
| Hazard Classification | High |
| Condition Assessment | Not Available |
| Last Inspection | 03/20/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL00518 |
| Federal ID | IL00518 |
| More Info | State Dam Safety Program |