As far as I can tell, the only decent source of data about which roads are dirt and which are paved is county road maps, and they often can be hard to get in print and forget on-line, the counties don't do that. Really and for a lot of rural area's where the roads are dirt, it's the county (or sometimes local town) that decides whether to lay asphalt or not. The counties are also deciding all the time to make what has been a dirt road, into a paved road.
None of the on-line map companies and websites are able to keep up with this, neither is Google satellite in my experience.