State Route 123 is a state highway in southwestern Ohio. The route runs from SR 251 about seven miles (11 km) southeast of Blanchester to Germantown at SR 4, a distance of 43.6 miles (70.2 km). The section of road from Franklin to Lebanon was originally a toll road until it was taken over by Warren County and made free for public use.

State Route 4, formerly known as Inter-county Highway 4 until 1921 and State Highway 4 in 1922, is a major north–south state highway in Ohio. It is the fifth longest state route in Ohio. Its southern terminus is at U.S. Route 42 in Cincinnati, Ohio, and its northern terminus is at U.S. Route 6 in Sandusky, Ohio. Its path is nearly ruler-straight for many miles. Some portions of the route are still marked as Dixie Highway. The northern portion was constructed by the Columbus and Sandusky Turnpike Company, see Turnpike Lands.