State Route 126 is a state route starting at the Ohio-Indiana border, at a split with State Route 129 near Scipio, Ohio, and ending east of Cincinnati at an intersection with U.S. Route 50 in Milford.

State Route 126 is locally known for comprising most of Ronald Reagan Cross County Highway, a freeway that splits off south Interstate 275 west of Cincinnati, crosses Interstate 75, and ends shortly after an intersection with Interstate 71. The westernmost portion of the highway is designated, but not signed, as Hamilton County Route 453. Ronald Reagan Highway was originally planned to extend eastward to Milford, but local opposition to the project in Indian Hill forced planners to abandon the segment east of Montgomery. Instead, it continues past Interstate 71 as a short divided highway until it merges with Montgomery Road (U.S. Route 22/State Route 3) near the Montgomery Heritage District.

List of unused highways in Ohio