Mapquest says it is about 1019 miles between the two cities (about 16 hours driving time), so the half-way point would be near the middle of Missouri.
If you are looking for a place to stop during a drive at the half-way point, you could stop anywhere between St Louis, MO and Springfield, MO. Some towns about half-way between there are: Rolla, St Robert (Fort Leonard Wood), and Lebanon, MO.
The major airport about half-way is at St Louis. Other airport half-way options would be Kansas City, Fort Leonard Wood, and Springfield, MO.
Washburn, TX is the halfway point.
The halfway point between Dallas, Texas and Warren, Ohio is in Centerville, Tennessee.
Amarillo, TX
Wills Point
Hewitt, Texas
Waco!
Turrell, AR
1/2 is the halfway point
Mayperal or mile marker 301
Huntsville, Mississippi
Martin, Tennessee.
Jackson, TN