Longview TX or Marshall TX
There are no towns halfway between a single place.
The city that is roughly halfway between Meridian, MS, and Baltimore, MD, is around Chattanooga, TN. This city is located along a common route taken when traveling between the two locations and serves as a convenient midpoint. Depending on the specific route chosen, other nearby towns may also be considered as possible halfway points.
Lavonia, Georgia, is halfway between those two towns.
Parkton, MD
Assuming you mean what town is halfway between Denver and Galveston. A small town named Childress is halfway, but the closest larger towns are Amarillo or Wichita Falls
There aren't many towns on that whole stretch of I-5. Wasco is the closest to halfway.
I-40 and I-20 are essentially the same time. I-40 - Jackson, TN is halfway (though you could stop in Memphis or Nashville if looking for larger cities) I-20 - middle of nowhere AL is halfway...though Tuscaloosa, AL or Meridian, MS are the largest cities/towns around the halfway mark. If you're looking for a city then shoot for Jackson, MS or Birmingham, AL.
New England, ND
Harrisonburg and Staunton, Virginia
Philadelphia is the city that is halfway between Washington DC and Boston MA. New York and Baltimore are the other towns that are in between.
Timaru is closest town to halfway between the two towns. It is 167 km from Christchurch and 192 km from Dunedin .
Halfway between Pensacola, FL, and Killeen, TX, lies the town of Vicksburg, MS. Another option is Monroe, LA, which is also approximately equidistant between the two cities. These towns provide convenient stopping points along the route.