The limestone zone of south-central Indiana was a natural area in which to build shelters or take refuge.  As such, The Apocalypse heavily bombarded it.  After the Final War, the few survivors filtered out and went in search of habitable land.  They found that in the Wabash River Valley they could eke out a living.
 
At the same time, survivors from Fortress Wayne left that poisoned town and moved out to the north and east, seeking not-too-destroyed lands at the edge of the ruined deathland that had been southern Michigan.

Blasted Lands - The making of Detroit/Destroyt and an intense mid-Final War battle across southern Michigan left a residue of radioactivity and earth poisons that exceeded the Ancients' ability to fix.  This zone extends from Destroyt westward across the whole Michigan peninsula, and around the southern edge of Lake Michigan to encompass the ruins of Chicago.  The survivors just called the area the Blasted Lands and as far as they are concerned it is the northern edge of the world.  Nasty creatures, monstrous horrors of genetic mutation, occasionally come out of the region, but nobody has ever gone exploring into it, nor crossed to the other side (if there is one) and returned to tell Wabash folk the tale.

Destroyt - The more things change, the more they stay the same.  By 2300, the Detroit area was again the single biggest manufacturer of vehicles in the world.  This production capacity could easily be turned into war vehicles if needed; Detroit was a high-priority target.  The city was eventually nuked so heavily that it does not just glow in the dark - it glows (casts a visible shadow and everything) in the day, too!  Note that the ruins are in the lake.  Travel to and from the ruins must be by boat.
Indianapolis - Like most other political capitals, this city was blasted from early on in the Final War.  Today, the Seekers claim the ruins and have done a good job of destroying what was left.  They have agreed to leave the Ancients' roadways for last.

Markle - This new city takes advantage of its position as a crossroad of river and Ancient road.  It is actively trying to bring the peoples to the north and east into its economic and political orbit.  It is not quite in the same place as the Ancient village of the same name.
Newport - This town can be reached (carefully) from the great Lake's shore.  It is the Lakeside entrepot to the Radioactivists' portage.  The town was built where the Ancient right-of-way enters the lake.  It IS slightly radioactive.  Roll once per day.

North Webster - The Beacons of Hope have a post here and maintain a school.

Old I-69 - This stretch of old highway has been found by the Beacons of Hope and renamed "Clinton's Road of Shame".  (The reason is not a secret but it is an inside joke.  A number of the old highway markers remain along its length.)  They use this path for a symbolic journey.  The village along its path contains an inn with hookers available.  The students and their teachers stay the night there.  All members of the party are expected to NOT indulge.  At the end of the road, the students are told they must choose the path they will take in life.  Then they are left to make a decision.  It is a bad sign if a student turns back the way he just came; he is heading back into Shame.  If he moves towards the Blasted Lands a little way to the north and west of here, it is a sign that he is enterprising and should be watched; he will either become great or he will destroy himself.  If he heads towards the nearby town, it is not an indication of anything; the student is not particularly original.
Plymouth - Only a Radioactivist would be dumb enough to live in the Blasted Lands, which the area northwest of this town is.  They do a booming business as middlemen between the Wabash peoples and those who travel the great Lake.  Plymouth is the Wabash entrepot to their portage.  Most people think that the Radioactivists' tales of the Lake's size are wildly exaggerated.  The area is not too radiated, having about the minimum necessary to be considered a Deathland.

Purroo - The old town of Peru has been discovered and settled by a number of feline races.  Most are descedants of the common house cat, but there is some lynx and bobcat blood also.  The current ruler is a Mutated Mountain Lion.  The town government is establishing an outbreeding program to spread the blood of the larger cats throughout the population.  They also secretly hope to one day breed the legendary feline warrior-race, the Kzinti.  The old town itself is used for residences and the area across the former riverbed is a hunting preserve, well-stocked with mice and rats and their descendants (including Squeekers).

Wabash - This ex-Ancient town has been rehabilitated by the Knights of Genetic Purity.  They claim to be the "Wabash County Restored Government" and assert claim to its whole territorial extent.  They have tried to revive the old names of ruins and places.  They have only been working on the area between the river and the road.
Wayun - Extensive ruins exist here, but they are still permeated with the residue of powerful and toxic nerve gasses.  These gasses affect any sentient being, but brute animals (and plants) are unaffected.

The area south of an east-west line drawn through Indianapolis is considered Taboo (echoes of memory from just after the Final War).  The lower Wabash River moves into a low-lying swampy area and forms a natrual impediment to travel, so nobody has explored downstream.  Unknown to the common Wabash inhabitant, the southern half of Indiana has multiple secret bases for the various Cryptic Alliances.  It also completely lacks any roads, trails, &c.

The old interstate right-of-ways have a thin layer of dirt on them, so grass grows (not bushes or trees) and are natural travel paths even today.  Sometimes a tree will force its way through broken pavement, but this type of barrier can be gotten around.  Broken bridges are another matter entirely.  Trees do grow on the raised berms and in the old median strips.  The ideal archetype has two ribbons of grass flowing through the forest.

There is a transition from forest to prairie as one moves to the lower Wabash.  This transition zone is about 50 kilometers wide.