Johnston City Lake Dam
Johnston City Lake Dam is an earth dam located in Williamson County, Illinois, built in 1921. It carries a Significant hazard potential classification.
About Johnston City Lake Dam
The primary purpose of Johnston City Lake Dam is water supply. The dam stores water for municipal, industrial, or agricultural use, helping ensure a reliable supply for the surrounding area. The dam is owned by City Of Johnson City (local government). It impounds the Trib Lake Creek near Johnston City.
The dam stands 14 feet tall and stretches 855 feet across, and has a maximum storage capacity of 601 acre-feet. Completed in 1921, 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. The most recent inspection on record was 04/23/2025.
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Location
| State | Illinois |
| County | Williamson |
| Nearest City | Johnston City |
| River/Stream | Trib Lake Creek |
| Coordinates | 37.80238, -88.86662 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 14 ft |
| Dam Height | 14 ft |
| Dam Length | 855 ft |
| Year Completed | 1921 (105 years old) |
Storage & Hydraulics
| NID Storage | 601 acre-ft |
| Max Storage | 601 acre-ft |
| Normal Storage | 466 acre-ft |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Water Supply |
| Owner | CITY OF JOHNSON CITY |
| Owner Type | Local Government |
| Hazard Classification | Significant |
| Condition Assessment | Not Available |
| Last Inspection | 04/23/2025 |
| Emergency Action Plan | No |
Identifiers
| NID ID | IL00048 |
| Federal ID | IL00048 |
| More Info | State Dam Safety Program |