There are
1,592 mi
from Harlingen, TX to Monrovia, CA
That's the driving distance. It would take 1 day 3 hours to go from Harlingen, Texas to Monrovia, California.
The flight distance (direct flight from Harlingen, TX to Monrovia, CA) is 1,328.39 mi.
1,592 mi = 2,561.92 kms