Keyhole State Park, State park in Crook County, Wyoming, US

Keyhole State Park is a 14,720-acre Wyoming state park in Crook County surrounding the 13,700-acre Keyhole Reservoir, formed by the 1952 Keyhole Dam on the Belle Fourche River. The park lies at about 1,250 meters and is reached via Interstate 90. It has nine campgrounds, a marina, and five hiking trails.

In the 1950s, the federal government built a dam in this area to manage flood risk and secure water supply for the region. The reservoir that formed behind the dam was later opened to the public as a state park.

Bird watchers come to the park throughout the year to take part in banding sessions where birds are caught, tagged, and released to track migration. More than 200 bird species have been recorded around the reservoir, making it a draw for anyone interested in wildlife.

The park is open year-round, but most facilities and camping areas operate only during the warmer months. It is worth checking which areas will be open before planning a visit, especially for those who want a specific type of site.

The reservoir's water is allocated by interstate compact: 90 percent goes to South Dakota and 10 percent to Wyoming, even though the reservoir lies entirely in Wyoming. The park is named after a ranch brand, not a physical keyhole.