There are
1,683 mi
from Allentown, PA to San Marcos, TX
That's the driving distance. It would take 1 day 6 hours to go from Allentown, Pennsylvania to San Marcos, Texas.
The flight distance (direct flight from Allentown, PA to San Marcos, TX) is 1,461.31 mi.
1,683 mi = 1.61 kms