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).

[2] Ohio Historical Marker #2-14 is located on State Route 123 near Blanchester.

[3] In Lebanon, SR 123 was rerouted to a new roadway, which the city of Lebanon has called "Neil Armstrong Way", from SR 63's (Main Street) intersection with Glosser Road to SR 123's existing intersection with Hart Road.

Armstrong for many years owned a farm along SR 123 between Lebanon and the community of Red Lion.

There are also plans to introduce a bill in the state senate to apply the name "Neil Armstrong Way" to the entire stretch of SR 123 from Lebanon to Red Lion.