In 1860, the southern edge of settlement— which delimited the “settled” areas with more than two persons per square mile from the “frontier” areas with fewer than two inhabitants per square mile— stood in central Florida. With the exception of a settled enclave about eastern Tampa Bay, the southern half of the Florida peninsula was a true frontier. It was the largest remaining frontier east of the Mississippi River. By 1860, the bulk of the south Florida frontier fell within the boundaries of five counties— Hillsborough, Manatee, Monroe, Brevard, and Dade whose total population was only 7,077.
Otto, John Solomon
"Florida's Cattle-Ranching Frontier: Hillsborough County (1860),"
Florida Historical Quarterly: Vol. 63
, Article 6.
Available at: https://stars.library.ucf.edu/fhq/vol63/iss1/6