Maryland Route 543 (MD 543) is a state highway in the U.S. state of Maryland. The state highway runs 19.08 miles (30.71 km) from U.S. Route 40 (US 40) in Riverside north to MD 165 in Pylesville. MD 543 is a north–south highway through central Harford County that connects the communities of Creswell, Fountain Green, Hickory, and Ady with the county's four main east–west highways: U.S. Route 40, Interstate 95 (I-95), MD 22, and US 1. MD 543 was originally constructed in the early 1930s from Hickory to north of Ady, where the highway followed part of what is now MD 646. The state highway swapped routes with MD 646 to end in Pylesville by 1946. MD 543 was extended south in three steps to MD 7 in the 1950s. The state highway was rerouted at its southern end when I-95 was constructed in the earl