Thunderbird Lake 1 Dam, located in McHenry, Illinois, is a privately owned earth dam constructed in 1965 for recreational purposes on Sleepy Hollow Creek. Standing at a height of 7 feet and a length of 420 feet, the dam has a storage capacity of 395 acre-feet, with a primary purpose of providing recreational opportunities to visitors. The dam's spillway is uncontrolled with a width of 21 feet, and it is classified as having a low hazard potential and moderate risk assessment.

While the dam is state-regulated and inspected, its current condition assessment is not available, and there is limited information on emergency preparedness measures such as an Emergency Action Plan (EAP) or inundation maps. Despite these gaps, Thunderbird Lake 1 Dam continues to serve as a popular recreational spot in the region, offering a picturesque setting for water resource and climate enthusiasts to enjoy outdoor activities. The dam's historical significance, combined with its scenic location and moderate risk assessment, make it a notable site for those interested in the intersection of water management and environmental conservation.