Watonwan County is a county located in the U.S. state of Minnesota. As of 2010, the population was 11,211. Its county seat is St. James. The county was organized in 1860, two years after Minnesota was granted statehood.
According to the U.S. Census Bureau, the county has a total area of 440 square miles (1,139 kmē), of which 435 square miles (1,125 kmē) is land and 5 square miles (14 kmē) (1.23%) is water. The county is drained by the Watonwan River and its tributaries; the river flows eastwardly through the northern part of the county.