How many acres in the largest ranch of South Dakota?

141,357 acres in the Bad River Ranches, I think.

Taking a lead from schumacher I discovered that the Bad Rivers Ranches is 141,357 acres. 220.870 sq. mi. Owned by Ted Turner. That is a lot of land. It might be the correct answer unless someone finds a bigger one.
https://www.tedturner.com/turner-ranches/turner-ranch-map/bad-river-ranch-south-dakota

Ted Turner owns more than two million acres making him the largest private landowner in the USA.
http://www.landreport.com/americas-100-largest-landowners/

He owns land greater than the size of Rhode Island. It is 988,800 acres or 1,545 sq. mi. Also, larger than Delaware, 1,592,960 acres or 2,489 sq. mi.
https://en.wikipedia.org/wiki/List_of_U.S._states_and_territories_by_area