There are
1,866 mi
from San Marcos, CA to Swansea, IL
That's the driving distance. It would take 1 day 8 hours to go from San Marcos, California to Swansea, Illinois.
The flight distance (direct flight from San Marcos, CA to Swansea, IL) is 1,560.91 mi.
1,866 mi = 1.61 kms