Indiana State Route 18 runs east-west across northern Indiana, nearly spanning the entire width of the state with no interruptions. The route reaches the western border near Freeland Park, where it becomes an Iroquois County highway (number 9, to be specific), but the eastern end at US Route 27 in Bryant is cut off by a persistent Indiana Route 67 that takes over the designation of the eastbound roadway. Indiana State Route 18 passes through many towns, including Fowler, Delphi, Marion, and Montpelier.