There are
1,278 mi
from Thornton, CO to Issaquah, WA
That's the driving distance. It would take 22 hours 4 mins to go from Thornton, Colorado to Issaquah, Washington.
The flight distance (direct flight from Thornton, CO to Issaquah, WA) is 999.99 mi.
1,278 mi = 1.61 kms