Lyon County is a county located in the U.S. state of Minnesota. As of 2000, the population was 25,425. Its county seat is Marshall.

According to the U.S. Census Bureau, the county has a total area of 721 square miles (1,869 km²), of which 714 square miles (1,850 km²) is land and 7 square miles (19 km²) (1.01%) is water.

Official Lyon County website