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.
EB I-74/SB U.S. Rt. 421 at the Shelby/Decatur County Line. EB I-74/SB U.S. Rt. 421 east of St. Paul. EB I-74/SB U.S. Rt. 421 east of St. Paul. WB I-74/NB U.S. Rt. 421 west of Greensburg. A BGS on EB I-74/SB U.S. Rt. 421. A BGS on WB I-74. SB U.S. Rt. 421 near Michigan Ave. SB U.S. Rt. 421 west of IN St Rt 3. SB U.S. Rt. 421 east of IN St Rt 3. SB U.S. Rt. 421 west of Ireland. SB U.S. Rt. 421/EB IN St Rt 46 west of Broadway.
