U.S. Federal Route 421 runs from the northwest part of Decatur County to the southeast. It goes from the Rush/Decatur County Line, near Middletown, to the Decatur/Ripley County Line, near Napoleon. U.S. Rt. 421 passes through the following towns in Decatur County. Greensburg Layton Mills Smyrna U.S. Rt. 421 is multi-plexed in Decatur County. Interstate 74, from the Rush/Decatur County Line to Greensburg.