Cox Lake Dam is an earth dam located in Wayne County, Illinois, built in 1959. It carries a Significant hazard potential classification.
Dam profile
NID height · 18 ft18 ft tall and 485 ft long. 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 Cox Lake Dam
The primary purpose of Cox Lake Dam is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Joe Williams (private). It impounds the Trib Watson Creek near Barnhill-offstream.
The dam stands 18 feet tall and stretches 485 feet across, and has a maximum storage capacity of 130 acre-feet. Completed in 1959, 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. The most recent inspection on record was 07/29/2025.
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Location
| State | Illinois |
| County | Wayne |
| Nearest City | Barnhill-offstream |
| River/Stream | Trib Watson Creek |
| Coordinates | 38.31551, -88.35569 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 18 ft |
| Dam Height | 18 ft |
| Dam Length | 485 ft |
| Year Completed | 1959 (67 years old) |
Storage & Hydraulics
| NID Storage | 130 acre-ft |
| Max Storage | 130 acre-ft |
| Normal Storage | 80 acre-ft |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Recreation |
| Owner | Joe Williams |
| Owner Type | Private |
| Hazard Classification | Significant |
| Condition Assessment | Not assessed |
| Last Inspection | 07/29/2025 |
| Emergency Action Plan | No |
Identifiers
| NID ID | IL00403 |
| Federal ID | IL00403 |
| More Info | State Dam Safety Program |