In South Dakota, you can ride an ATV along the ditches of any road or highway, except an Interstate Highway. However, the Transportation Commission or a county's board of commissioners can restrict ATVs from riding in certain ditches. ATVs are not allowed on snowmobile trails or any land controlled by the Department of Game, Fish and Parks, except in designated off-road areas. There are several areas on state and federal land where you can legally operate your ATV. Visit the Department's website for more information. To operate an ATV in a state park or on state land, it must be registered as a motorcycle or possess a state park license. The operator must be at least 14 years of age, wearing a helmet, and possess a valid driver's license. An ATV licensed as a motorcycle may never be driven on an interstate highway.
Check out these Philip, SD ATV/OHV resources: