Location: Conowingo Rd and Castleton Rd, Harford Cty Just after 161, we’ll approach MD 623. Location: Conowingo Rd and Castleton Rd, Harford Cty Turn right for 623 east, which is a short spur back to Darlington. Location: Conowingo Rd and Castleton Rd, Harford Cty Turn right for 623 east/south. Turn left for 623 north.  N … Continue reading U.S. Route 1, MD-161 to MD-623