and was organized on December 13, 1879 with De Smet as the county seat. Settlements at Lake Preston, Arlington, and Iroquois grew rapidly, driven by the railroad and fertile prairie lands. By 1880, the county's population reached 1,234.

Agriculture, particularly corn and wheat, anchored early economic growth, with towns like Lake Preston boasting mills and newspapers by 1881. De Smet gained fame as the setting for Laura Ingalls Wilder's Little House series, including The Long Winter