Check out this visual map of all the McDonald's in America - I found it on 74 Lime Lane, it was put together by Stephen Von Worley with an interesting article that is worth the read here.
The author tried to find the McFarthest spot, the area of the country with the widest gap in between McDonald's locations. The McFarthest spot was 145 miles even in the most rural hills of the Dakotas. Pretty scary!!