There are
1,644 mi
from Great Falls, MT to Harker Heights, TX
That's the driving distance. It would take 1 day 5 hours to go from Great Falls, Montana to Harker Heights, Texas.
The flight distance (direct flight from Great Falls, MT to Harker Heights, TX) is 1,344.13 mi.
1,644 mi = 2,645.06 kms