Assuming you're taking I-44, the halfway point is near Plano, Missouri but locations in the west part of Springfield are close enough.
Lakenan, Missouri is the halfway point.
Sierra Blanca, TX
Morton, IL
Van Horn, TX
Kansas
Around/between Charleston and Arcola IL, depending on what route you take.
The halfway point between Peoria and Topsail Island is Point Pleasant, WV, on US-35 just on the West Virginia side of the Ohio state line. (Route highlights: I-74 to I-70 to US-35 to I-77 to I-74 to I-40)
According to MeetWays, halfway between Cheyenne, Wyoming and Wichita, Kansas would be a point near Brewster, Kansas on I70.
Kansas City, Missouri.
Salina Kansas
The halfway point between Melbourne and London is Akyab, Myanmar.
Westfall, Kansas.
Rishel, Kansas.
Terre Haute, IN