A fire broke out in an open shed filled with around 1,900 hay bales near the intersection of Highway 50 and 454th Avenue east of Gayville on Saturday morning.
Fire departments from Gayville, Yankton, Wakonda, Volin, and Vermillion responded to the scene.
Despite heavy fog making it difficult to spot the fire initially, efforts were made to prevent the blaze from spreading to a nearby barn.
The fire is believed to have been caused by a build-up of heat in the hay.
Firefighters worked until 2 p.m., and the owners will continue to monitor the remaining hay for any potential flare-ups.
No injuries were reported.