There are
1,548 mi
from Great Falls, MT to Duncanville, TX
That's the driving distance. It would take 1 day 3 hours to go from Great Falls, Montana to Duncanville, Texas.
The flight distance (direct flight from Great Falls, MT to Duncanville, TX) is 1,272.84 mi.
1,548 mi = 2,490.87 kms