In Georgia, I'll list Baldwin, Ben Hill, Burke, Colquitt, Dougherty, Glascock, Hancock, Irwin, Jefferson, Johnson, Putnam, Telfair, Worth (and possibly Screven save for those old enough to have traveled before I-95).
Baldwin- I've been to Millidgeville several times.
Dougherty- I went to Albany once when I was young, I think.
Johnson- I've got an uncle in Wrightsville.
Putnam- I travel through whenever I go to my grandparents.
Telfair- I've got cousins in McRae. In addition, we pass through Telfair on the route my family usually takes to the beach.
I've passed through once, taking US 378 to Colombia.
Ive been to all of the counties in Florida. There has to be one that nobody's been to, maybe Alachua?
I actually just got home from a trip to Gainesville.
---
I don't know where all in the state Clay and Dibble have travelled, but I'll guess Gilmer, Murray, Oconee, Oglethorpe, Walton and Wheeler.