Keyhole State Park

Spanning nearly 16,000 acres on the western edge of the Black Hills, this state park centers on a massive reservoir known for premier walleye fishing, pine-shaded campgrounds, and a unique reservable treehouse.

Keyhole State Park encompasses 15,890 acres of water and pine-speckled prairie along the western edge of the Black Hills in northeastern Wyoming. The park centers on Keyhole Reservoir, a 14,000-acre body of water created by the damming of the Belle Fourche River. Completed by the Bureau of Reclamation in 1952, the earthfill Keyhole Dam was originally built for flood control and irrigation, resulting in a fascinating water-sharing agreement: by interstate compact, 90 percent of the reservoir's water is allocated to South Dakota, leaving 10 percent for Wyoming. The park itself takes its name from the historic "Keyhole" livestock brand once used by the McKean brothers, who operated a ranch on these lands before the reservoir drowned the valley. At an elevation of 4,100 feet, the park provides a refreshing aquatic playground in an otherwise arid grassland, with the distinctive fluted silhouette of Devils Tower visible on the northern horizon.

Anglers and boaters dominate the reservoir, which is renowned for yielding some of the largest sport fish in the state. The deep, cool waters support thriving populations of walleye, northern pike, smallmouth bass, yellow perch, and channel catfish, making it a premier destination for both summer casting and winter ice fishing. Along the southern shore, Keyhole Marina operates as a full-service hub, providing fuel, groceries, wet and dry boat slips, and rentals for boats and paddleboards. Beyond the water, the park is a major ecological sanctuary, serving as a vital stopover for over 225 species of resident and migrating birds. Visitors frequently share the shoreline with white-tailed deer, wild turkeys, and pronghorn, while the short Prairie Dog Town Trail offers close-up views of the area's industrious rodent colonies.

Accommodations within the park are spread across 10 distinct campgrounds containing over 300 campsites. Tatanka Campground is the primary choice for RV travelers, offering 32 sites equipped with water and electricity alongside modern, ADA-accessible restrooms and hot showers. For a more rustic experience, Cottonwood Campground offers direct shoreline access under a canopy of mature cottonwoods and ponderosa pines. Cottonwood is also home to Wyoming's first state park treehouse: a universally accessible, 576-square-foot cabin elevated six to ten feet off the ground, featuring two bedrooms, an electric fireplace, and a private deck overlooking the water. Four additional log cabins are available for year-round rental in the Tatanka area. Those looking for a quieter visit can explore the 1.5-mile concrete Marina Trail or keep an eye out for updates on the state's proposed new visitor center, planned for the Coulter Bay area.