The counties in North Carolina bordering Mecklenburg county (which includes Huntersville and Cornelius) include Cabarrus, Iredell, Lincoln, Gaston, and Union. York and Lancaster counties in South Carolina also border Mecklenburg county.
The best place to start would be to download the state map (which shows counties) here (on the right hand side):
NCDOT: State Transportation Map
This should also give you an idea of the distances from Huntersville/Cornelius since mileage is labeled on the map.