Starting some very preliminary planning for a family vacation in the summer of 2018 to include Springfield, IL, Louisville and Bowling Green, KY as well as Mammoth Cave, Nashville, TN and St. Louis, MO. Is the best route between Springfield, IL and Louisville really through Indianapolis? That's what keeps pulling up on a route planner, but seems quite a bit out of the way. Anyway know of a better route?

Online trip planners usually default to the fastest route not the shortest.
You can usually change what type of route you want in options in most map programs. Try mapquest, they usually provide a few routes.

You can actually "pull' the route line with your cursor