The Dakota Territory created the county on April 9, 1883, with areas partitioned from Ransom County, from previously unorganized areas and from non-county areas in the Wahpeton and Sisseton Indian Reserve. It was named for H. E. Sargent, a railroad executive. Its governing structure was not completed at that time, so it was attached to Richland for judicial purposes and to Ransom for administrative purposes. This arrangement only lasted until October 8, when the county government was effected, with Milnor as the county seat. However, in 1884, in the county's first election, Forman was chosen as the county seat.