Lake Hillsboro Dam is an earth dam located in Montgomery County, Illinois, built in 1917. It carries a Significant hazard potential classification.
Dam profile
NID height · 34 ft34 ft tall and 693 ft long, taller than 78% of U.S. dams with a recorded height. Height is drawn to scale against a two-story house, about 25 ft; the profile is a generic embankment section and the water level is illustrative.
About Lake Hillsboro Dam
The primary purpose of Lake Hillsboro 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 Hillsboro (local government). It impounds the Trib Middle Fork Shoal Creek near Hillsboro.
The dam stands 34 feet tall and stretches 693 feet across, creates a reservoir covering 107 acres, has a maximum storage capacity of 1,747 acre-feet, and collects water from a drainage area of 6 square miles. Completed in 1917, the structure is over a century 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 09/18/2025.
At 34 feet, this dam is taller than 78% of dams nationwide.
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 | Hillsboro |
| River/Stream | Trib Middle Fork Shoal Creek |
| Coordinates | 39.18006, -89.47873 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 34 ft |
| Dam Height | 34 ft |
| Dam Length | 693 ft |
| Year Completed | 1917 (109 years old) |
Storage & Hydraulics
| NID Storage | 1,747 acre-ft |
| Max Storage | 1,747 acre-ft |
| Normal Storage | 879 acre-ft |
| Surface Area | 107 acres |
| Drainage Area | 6 sq mi |
| Max Discharge | 3,276 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Recreation |
| Owner | City of Hillsboro |
| Owner Type | Local Government |
| Hazard Classification | Significant |
| Condition Assessment | Not assessed |
| Last Inspection | 09/18/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL00699 |
| Federal ID | IL00699 |
| More Info | State Dam Safety Program |