History

The park was established in 1982 with land acquired by Florida's Conservation and Recreational Lands program.

Now 2,421 acres on the northern third of the island of Key Largo, the park was named for Dagny Johnson, a local environmental activist, approximately one year before her death in 2003.

Throughout the 1970s-90s, Johnson led the Upper Keys Citizens Association, the Izaak Walton League and other environmental organizations that fought to stop the development that was planned for much of north Key Largo. Preservation of onshore communities was not the only purpose for protecting north Key Largo. These environmental activists also wanted to protect the coral reefs offshore from the adverse impacts of land development.