Presumably you mean Nashville, Tennessee.
If you mean Portland, Maine, the midpoint appears to be close to the Pennsylvania/West Virbinia line, southeast of Pittsburgh.
If you mean Portland, Oregon, the midpoint is in southeast Wyoming.
Portland, TN. Just over the border. It's between Bowling Green and Nashville.
What is the center point between Nashville, TN., Charleston, S.C., and New York City?
If Driving, the halfway point would be in-between Nashville, TN and Memphis, TN. There is no good town indicator. Mile 143 on I-40 might be a good halfway point.
Halfway point between Alabaster, AL and Portland, TN is Birmingham, AL.
The halfway point between Nashville, Tennessee and Philadelphia, Pennsylvania is Harmon Forest, Virginia.
Egypt
Nashville, TN
Chehalis!
Nashville, Tennessee is halfway between Buffalo & Houston
going on I65
Willisburg, Kentucky
Maps.google.com