State Route 42 (SR 42) is a 115.3-mile-long (185.6 km) state highway that runs southeast-to-northwest through portions of Peach, Crawford, Monroe, Butts, Henry, Clayton, and DeKalb counties in the central and north-central parts of the U.S. state of Georgia. The route connects Byron with the Atlanta metropolitan area, via McDonough, Stockbridge, and Forest Park.