Ortonville is a city in Big Stone and Lac qui Parle counties in the U.S. state of Minnesota at the southern tip of Big Stone Lake, along the border with South Dakota. The population was 1,916 at the 2010 census. It is the county seat of Big Stone County. Big Stone Lake State Park is nearby.
According to the United States Census Bureau, the city has a total area of 3.5 square miles (8.9 km²), of which 3.4 square miles (8.8 km²) is land and 0.1 square miles (0.1 km²) (1.45%) is water.
U.S. Routes 12 and 75 and Minnesota State Highway 7 are three of the main routes in the city.