State Route 189 is a 11.58-mile (18.64 km) long state highway in the northwestern portion of the U.S. state of Ohio. The highway runs from its western terminus at its junction with U.S. Route 224 (US 224) and SR 66 in Ottoville to its eastern terminus at the intersection of SR 115 and SR 12 in Vaughnsville, nearly 5 miles (8.0 km) southwest of Columbus Grove. SR 189 runs entirely within Putnam County and is entirely a two-lane highway.

U.S. Route 224 (US 224) is a spur of US 24 that runs through the states of Indiana, Ohio and Pennsylvania. It currently runs for 289 miles (465 km) from US 24 in Huntington, Indiana, east to US 422 Business and Pennsylvania Route 18 (PA 18) in New Castle, Pennsylvania. It goes through the cities of Canfield, Ohio, Akron, Ohio, and Findlay, Ohio. In Northeast Ohio, US 224 is located a short distance north of the Western Reserve's southern boundary.