What is the name of the Disney park in Florida that opened in 1971?

The Disney park in Florida that opened in 1971 is Magic Kingdom.

Magic Kingdom opened on October 1, 1971, as the first theme park at Walt Disney World Resort near Orlando, Florida. It was modeled in part on Disneyland in California, but its larger setting allowed Disney to create a more expansive resort destination. Cinderella Castle became its signature landmark, replacing Disneyland's Sleeping Beauty Castle as the visual centerpiece.

The park is organized into themed lands, including Main Street, U.S.A., Adventureland, Frontierland, Liberty Square, Fantasyland, and Tomorrowland. Main Street, U.S.A. leads guests toward Cinderella Castle, following the hub-and-spoke layout used in several Disney parks.

The wording matters: Walt Disney World Resort opened in 1971, but the specific park was Magic Kingdom. Epcot opened in 1982, Disney's Hollywood Studios opened in 1989, and Disney's Animal Kingdom opened in 1998. Those later parks are why the answer should not be generalized to “Walt Disney World.”