what can the county do if my shed violate zoning distance?
Usually the penalties are right there in the code. My town, it's a fine of  $50/day from the time it was built until the time it's corrected; i.e. not a trivial amount. It will vary with the Local Area Having Jursidiction (LAHJ) so only someone from your immediate area would know what might apply to you.

As with most laws, ignorance is not considered a valid excuse, and generally will not sway the zoning board (which is usually what holds sway over this sort of thing, in my area, anyway.)