Here's a video of some Chicago & North Western trains in Elroy, Wisconsin. Considering the fanfare at the beginning, the film probably begins with an inaugural run of the Dakota 400, which launched with diesel locomotives in 1950 and extended the route of the predecessor Minnesota 400 into South Dakota.
The route ran from Chicago through Madison to Winona, Minnesota, and then across the southern part of the state into South Dakota. At one point, it ran all the way out to Rapid City, a distance of around 900 miles (my book with the correct number is not handy at the moment). I believe it covered the distance in 24 hours, so this route wasn't particularly fast, only around 37 or 38 mph average speed.
The speed was partly due to lighter and cheaper rails used along the route, particularly from Winona on westward. Even today, Canadian Pacific and their subsidiary DM&E are still replacing the old light rail with heavier continuous welded rail. It also stopped fairly frequently, operating something more like a local train than an express.
The train eventually got cut back to Mankato, Minnesota and was renamed the Rochester 400. It stopped operating on July 23, 1963, the same day as the original 400 which ran from Chicago to the Twin Cities.