State Route 129 is an east–west highway in southwest Ohio running from its western terminus at SR 126 and Indiana State Road 252, just east of the Indiana–Ohio state line near Scipio, Ohio. Its eastern terminus is east of Interstate 75 (I-75) at Cox Road in Liberty Township. The route's eastern terminus was historically at SR 747 until 1999 when the route was moved south 1⁄2 mile (0.80 km) to the newly built Butler County Veterans Highway.

Interstate 75 (I-75) runs from Cincinnati to Toledo by way of Dayton in the US state of Ohio. The highway enters the state running concurrently with I-71 from Kentucky on the Brent Spence Bridge over the Ohio River and into the Bluegrass region. I-75 continues along the Mill Creek Expressway northward to the Butler County line just north of I-275. From there, the freeway runs into the Miami Valley and then passes through the Great Black Swamp before crossing into Michigan.