Which US national park is the only one named after a president?

The only US national park named after a president is Theodore Roosevelt National Park.

Located in western North Dakota, the park commemorates Theodore Roosevelt and the years he spent ranching and hunting in the Dakota Badlands. His experiences there helped shape his belief in conservation and influenced the environmental policies of his presidency from 1901 to 1909.

The park consists of the South Unit, North Unit, and Elkhorn Ranch Unit, all connected by the Little Missouri River landscape. It covers about 70,446 acres of colorful badlands, prairie, river valleys, and wildlife habitat. Bison, wild horses, elk, and prairie dogs are among its notable animals.

The site was first established as Theodore Roosevelt National Memorial Park in 1947; Congress added the North Unit in 1948. Its designation changed to national park in 1978. The wording can be confused with national forests and historic sites named for Abraham Lincoln or Franklin D. Roosevelt, but those are not US national parks.