The 1860 census rolls for Hillsborough and Manatee are readily accessible. They are not that lengthy and a search through the rolls can easily reveal those males of military age. Polk County was not created until 1861.
Spessard Stone has written an excellent account on the "Tories" of the lower Peace River Valley which is available online. Many members of the Whidden, Carlton, Hendry, Platt and other families supported the Union.
Even F.C.M. Boggess, later a Confederate officer in the Cow Cavalry, described himself as a Union man. Also Francis A. Hendry initially supported the Union and drove a hard bargain when he supplied the CSA with his beeves. I find it amusing that there are Sons of Confederate Veterans camps in Florida named for Boggess and Hendry.