Six cars of an eastbound BNSF grain train derailed about six miles east of Yankton.
Amy McBeth with BNSF says the cars went off the track about 11:45 Monday morning.
A worker at the scene says a broken rail was the most likely reason for the derailment.
The cars were all upright, and should be able to put back on the rails. Repairs should be completed by mid day Tuesday. The cars were near the end of the 114 car unit train.