Guernsey State Park, State park in Platte County, Wyoming, United States

Guernsey State Park surrounds the Guernsey Reservoir on the North Platte River, one mile northwest of Guernsey in Platte County, Wyoming. The park contains campgrounds, boat ramps and hiking trails, along with structures built by the Civilian Conservation Corps in the 1930s. The Guernsey Dam, 41 m high and 170 m long at its crest, impounds the reservoir.

The park's origin lies in the Guernsey Dam, built between 1925 and 1927 to impound the North Platte River. From 1934 to 1939, Civilian Conservation Corps crews built roads, bridges, cabins and the museum, the first collaboration between the National Park Service and the Bureau of Reclamation. Wyoming took over management in 1957, and the district was named a National Historic Landmark in 1997.

The Guernsey State Park Museum, built by CCC crews in 1936, covers the Civilian Conservation Corps and the natural and cultural history of the area. Nearby, the Oregon Trail Ruts keep the wheel tracks of wagon settlers carved into an eroded sandstone ridge, and Register Cliff lies two miles southeast of the park.

The park offers multiple campgrounds, boat ramps, and hiking trails scattered throughout the area for visitors to explore. Plan for changing weather, as conditions can shift noticeably depending on the season.

The park's buildings were constructed from local materials following specific design principles that earned recognition as a National Historic Landmark. This craftsmanship shows an approach to construction that is rarely seen in newer parks.