Willow Lake Dam
Willow Lake Dam is an earth dam located in Stephenson County, Illinois, built in 1974. It carries a High hazard potential classification.
About Willow Lake Dam
Willow Lake Dam is a dam in Stephenson, Illinois. The dam is owned by Willow Lake Association (private). It impounds the Trib Pecatonica River near Freeport.
The dam stands 25 feet tall and stretches 590 feet across, creates a reservoir covering 23 acres, has a maximum storage capacity of 299 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 1974, 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 08/13/2025.
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 | Stephenson |
| Nearest City | Freeport |
| River/Stream | Trib Pecatonica River |
| Coordinates | 42.33181, -89.63911 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 25 ft |
| Dam Height | 25 ft |
| Dam Length | 590 ft |
| Year Completed | 1974 (52 years old) |
Storage & Hydraulics
| NID Storage | 299 acre-ft |
| Max Storage | 299 acre-ft |
| Normal Storage | 165 acre-ft |
| Surface Area | 23 acres |
| Drainage Area | 0 sq mi |
| Max Discharge | 2,313 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Other |
| Owner | WILLOW LAKE ASSOCIATION |
| Owner Type | Private |
| Hazard Classification | High |
| Condition Assessment | Not Available |
| Last Inspection | 08/13/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | IL01205 |
| Federal ID | IL01205 |
| More Info | State Dam Safety Program |