Tierra Verde was once 15 islands covered with mangroves, pines and bush. These islands ranged in size from only a few acres to the largest, Cabbage Key, having over 289 acres (1.17 km2). For centuries, Indians used the islands for ceremonial and burial grounds. A marker remains on the east side of Pinellas Bayway, just north of East Shore Drive, where Indian relics were found in a typical shell mound, excavated when the road was built to Fort DeSoto Park. The islands were sacred ground to Indian nations as far back as 500 years ago, archaeologists suggest, and deadly conflicts occurred when outsiders trespassed.

Then the Spanish explorers came. One explorer, Ponce De Leon, came to the area in 1513, and again in 1521, when he received the wound that he later died from after returning to Cuba. Later, Hernando De Soto, Navarez and John Ortiz explored, and then pirates and buccaneers sailed the area, including Jose Gaspar, Juan Gomez and Jean LaFitte. A treasure was reputed to have once been buried here.

In 1848 Robert E. Lee, then a lieutenant colonel in the U.S. army, recommended that Mullet Key be used for coastal defense in Florida. During the Spanish-American War of 1898, Fort De Soto was built on Mullet Key. Remains of the fort still stand, along with fortifications on Egmont Key. In 1948 the federal government sold Mullet Key to Pinellas County for park and recreation facilities, now Fort De Soto Park.

Early settlers to the area included Baltimore sea captain William Bunce and Silas Dent, who with his brother had a dairy farm. Dent lived on Cabbage Key until he died there in 1952. The Roberts family was among the early settlers of Pass-A-Grille and Tierra Verde. George "Florida" Roberts was a fishing guide for figures such as land developer Walter Fuller, Cecil B. Detre, and John Wanamaker. The thousands of tarpon caught by Roberts and his clients can be found as far away as Alexandria, Egypt in the home of Sir Harry Rofe.

Although two homes were built on Monte Cristo in 1923, and one in 1946, things were quiet until the mid-1950s when a Dr. Bradley "Doc" Waldron went to Tallahassee and persuaded the State of Florida to sell him Pine Key, Cabbage Key, Pardee Key and the surrounding bay bottom. This was about the same time construction of the old Skyway Bridge began. Waldron formed a partnership with two builders from Detroit, Hyman and Irving Green, who became majority owners of a group of 36 corporations. They named their island investment "Green Land."

Waldron-Green Associates applied for a dredge-and-fill permit in 1957. Their intent: to pump some 9,000,000 cubic yards (6,900,000 m3) of sand and shells from the bottom of the bay and thus enlarge and raise the ground level of the three keys Doc Waldron had purchased from the State and join them to create one large island intersected with canals between the sections.

Meanwhile, others sought county and state permission to dredge and pump the bay bottom and build up Bird Key, today's Bayway Isles and Isla Del Sol. Miami developer Leonard Ratner purchased land which became the site of Eckerd College. Hamilton Disston, the largest landowner in the United States, began and lost his Disston City development, later renamed Gulfport.

At first, the only way to get here was by boat. A ferry ran from Pass-A-Grille to a dock at the end of Madonna Boulevard. Then the state developed its plans for the Bayway and financed it through a $16.8 million bond issue. The Greens persuaded the Department of Transportation to add a Fort DeSoto leg and contributed the land on which it was to be built, thus assuring themselves of land access to their proposed Tierra Verde.