State Route 189 (SR 189, OH 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 nearly 5 miles (8.0 km) southwest of Columbus Grove.

SR 189 runs entirely within Putnam County. There are no segments of SR 189 that are included as a part of the National Highway System (NHS). The NHS is a network of highways that are identified as being most important for the economy, mobility and defense of the nation.

The SR 189 designation was applied in 1923. It was originally routed from Columbus Grove to the former SR 5 near Delphos.

SR 189 was extended in 1925, routed from SR 115 near Columbus Grove to SR 190. Then, in 1932, the road was extended to SR 190 to SR 66 in Ottoville.

The entire route is in Putnam County.