Walter J. Hayes State Park is a public recreation area covering 654 acres (265 ha) on the southeast corner of Wamplers Lake in the Irish Hills region of the state of Michigan. Most of the state park lies within Lenawee County with a small portion extending into Jackson and Washtenaw counties in the Round Lake area. The park offers access to 796-acre (322 ha) Wamplers Lake and completely surrounds 100-acre (40 ha) Round Lake, which connects to Wamplers Lake via a channel navigable by smaller boats. Other scenic lakes including Evans Lake and Sand Lake as well as chains of smaller lakes lie nearby. The park is traversed by Michigan Route 124 north of its intersection with US Highway 12.

Lenawee County is a county located in the U.S. state of Michigan. As of the 2020 United States Census, the population was 99,423. The county seat is Adrian. The county was created in 1822, from territory partitioned from Monroe County. Its governing structure was organized in 1826.