Complex sentence: The city of Key West is the county seat of Monroe County, which consists of a section on the mainland which is almost entirely in Everglades National Park, and the Keys islands from Key Largo to the Dry Tortugas.
Split into simpler sentences: The city of Key West is the county seat of Monroe County. The county consists of a section on the mainland which is almost entirely in Everglades National Park, and the Keys islands from Key Largo to the Dry Tortugas.