There are
1,670 mi
from Great Falls, MT to Clarksville, IN
That's the driving distance. It would take 1 day 5 hours to go from Great Falls, Montana to Clarksville, Indiana.
The flight distance (direct flight from Great Falls, MT to Clarksville, IN) is 1,431.70 mi.
1,670 mi = 2,687.61 kms