High Quality Content by WIKIPEDIA articles! Maryland Route 24 (MD 24) is a state highway in the U.S. state of Maryland. The state highway runs 25.17 miles (40.51 km) from an entrance to Aberdeen Proving Ground in Edgewood north to the Pennsylvania state line near Fawn Grove, Pennsylvania. MD 24 is the main north–south highway of Harford County. The southern half of the state highway connects U.S. Route 1 (US 1) and the county seat of Bel Air with Aberdeen Proving Ground, US 40, and Interstate 95 (I-95) through a suburban corridor. The northern half of MD 24 is a rural highway that passes through Rocks State Park.