Conservationist M.C. Davis of Santa Rosa Beach is donating a 1,500-acre easement of Walton County land to the state.
The land, which sits just east of Freeport, could have sold for an estimated $12 million.
The easement means the land can't be sold or developed and can only be used as part of the greenway.
The greenway is a 100-mile land corridor established to preserve the Panhandle environment and stop developers from encroaching on military installations, hindering their operations.