State Route 181 (SR 181) is a 4.46-mile (7.18 km) long east–west state highway in the northern portion of the U.S. state of Ohio. The western terminus of SR 181 is at a signalized intersection with SR 61 in downtown Crestline, and its eastern terminus is at a T-intersection with SR 309 approximately 1 mile (1.6 km) west of Ontario.Designated in the middle of the 1920s, SR 181 primarily serves as a short route connecting traffic between Crestline and Ontario.