The Capitol 400 was a streamlined passenger train operated by the Chicago and North Western Railway between Chicago, Illinois and Madison, Wisconsin via Milwaukee, Wisconsin.

From Madison it returned to Chicago via Janesville, Wisconsin.

In January 1942, just after the entry of the United States into World War II, the Chicago and North Western received four new streamlined trainsets.

The two remaining sets were pooled to provide a variety of services between Chicago and various destinations in Wisconsin: Milwaukee (Commuter 400 and City of Milwaukee 400), Green Bay (Shoreland 400 and Valley 400) and finally Madison: the Capitol 400.

[2]: 799–810  On April 30 the North Western discontinued the Capitol 400, replacing it with the Dakota 400, which originated in Huron, South Dakota and operated to Chicago via Madison in both directions.