Google maps with driving directions and county lines
As you pan around North America, all of the county lines for the area in view will be drawn. Clicking the Analyze button will create a report for your route, showing distance, duration, and counties that the route passes through.
The page can be flaky about adding "waypoints" to your route. You may have better luck if you add waypoints as soon as the page loads and before the county lines are drawn. It may also be easier to enter arbitrary waypoint locations below and move them after the map loads. Google limits the number of driving direction requests we can make each day. This feature may be unavailable at times if it gets too popular.
Send bug reports and feature requests to firstname.lastname@example.org.