Thunderbird Lake 2 Dam is an earth dam located in McHenry County, Illinois, built in 1965. It carries a Low hazard potential classification.
Dam profile
NID height · 10 ft10 ft tall and 360 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 Thunderbird Lake 2 Dam
The primary purpose of Thunderbird Lake 2 Dam is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Charles F. Wirth (private). It impounds the Sleepy Hollow Creek near Barreville-offstream.
The dam stands 10 feet tall and stretches 360 feet across, and has a maximum storage capacity of 395 acre-feet. Completed in 1965, the structure is well into its service life at over 50 years old.
This dam has a low hazard potential classification, meaning that failure would cause minimal damage, limited primarily to the dam owner's property, with no expected loss of life. The most recent inspection on record was 10/03/2025.
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Location
| State | Illinois |
| County | McHenry |
| Nearest City | Barreville-offstream |
| River/Stream | Sleepy Hollow Creek |
| Coordinates | 42.27499, -88.26902 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 10 ft |
| Dam Height | 10 ft |
| Dam Length | 360 ft |
| Year Completed | 1965 (61 years old) |
Storage & Hydraulics
| NID Storage | 395 acre-ft |
| Max Storage | 395 acre-ft |
| Normal Storage | 220 acre-ft |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Recreation |
| Owner | Charles F. Wirth |
| Owner Type | Private |
| Hazard Classification | Low |
| Condition Assessment | Not assessed |
| Last Inspection | 10/03/2025 |
| Emergency Action Plan | No |
Identifiers
| NID ID | IL01126 |
| Federal ID | IL01126 |
| More Info | State Dam Safety Program |