Whitman's son-in-law told the BBC the singer died of heart failure at Orange Park Medical Center in Jacksonville.
The Word War II veteran was discovered in 1948 by music manager Colonel Tom Parker, who also helped performers such as Minnie Pearl, Hank Snow, Eddy Arnold and Elvis Presley kick off their careers, the Florida Times-Union said.
Among Whitman's hits were "Love Song of the Waterfall," "Indian Love Song," "Rose Marie," "Cattle Call," "Tumbling Tumbleweeds," "Danny Boy," "Vaya Con Dios," "Kathleen," "Secret Love" and "Una Paloma Blanca."
Whitman -- whose real name was Ottis Dewey Whitman Jr. -- released his final album, "Twilight on the Trail," in 2010. It was his first new set of recordings in 26 years, the Times-Union said.
There were conflicting reports on his age, with some obituaries listing him as 89 when he died.