Sanborn County is a county in the U.S. state of South Dakota. As of the 2020 United States Census, the population was 2,330. Its county seat and largest city is Woonsocket. The county was created by the Dakota Territorial legislature on May 1, 1883 with land partitioned from Miner County. It was fully organized by July 18, 1883.
The terrain of Sanborn County consists of rolling hills, largely devoted to agriculture. The James River flows southward through the east-central part of the county, and the SW part of the country is drained by Dry Run Creek. The terrain slopes to the south and to the southeast; its highest point is in its SW corner, at 1,358′ (414m) ASL. The county has a total area of 570 square miles (1,500 km2), of which 569 square miles (1,470 km2) is land and 1.2 square miles (3.1 km2) (0.2%) is water.