When my reps create a contact or account.  I would like for them to pick a STATE  (example IDAHO) from drop down.

Then If they select IDAHO  another field will show  County Name  (ie. Bonneville, Freemont, Madison)

See Photo of Table.

So Field County should only show COUNTIES that map to IDAHO.

Custom Function may or may not work. So the real question is how to make it dynamic while filling out a form.