State Route 166 (SR 166) is an east–west state highway in the northeastern portion of the U.S. state of Ohio. The western terminus of State Route 166 is at a T-intersection with U.S. Route 6 just over 3 miles (4.8 km) northeast of Chardon. Its eastern terminus is at State Route 534 about 5 miles (8.0 km) west of Rock Creek.