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, `80s and `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.
Remnants of the Port Bougainville development still existed in the park in 1988. This included roadways, parking lots, buildings and other structures. The park has removed most of these and replanted the affected areas with native plants.
Buildings of the former Port Bougainville development were visible prior to restoration work. Contrast this older photo with the aerial banner photo on the homepage. The park contains the largest contiguous tract of West Indian tropical hardwood hammock in the United States.
In 2001, the park's name was changed to honor the activist who spearheaded the citizens' group largely responsible for the state's move to acquire the property. Shown from left to right in this photo of the dedication ceremony are Dagny Johnson, State Representative Ken Sorenson and former District 5 Bureau Chief, George Jones (at microphone).
At the park's main entrance, one can take a self-guided nature walk along the paved path. No motorized vehicles are allowed beyond the parking lot, making for a quiet repose with nature.