There are
1,832 mi
from Great Falls, MT to Port Lavaca, TX
That's the driving distance. It would take 1 day 8 hours to go from Great Falls, Montana to Port Lavaca, Texas.
The flight distance (direct flight from Great Falls, MT to Port Lavaca, TX) is 1,523.87 mi.
1,832 mi = 2,948.66 kms