New Castle, DE County Courthouse - Photo by Delaware Greenways New Castle City and the location of the historic New Castle County Courthouse (ca.1732). It was designated a National Historic Landmark in 1972 for its historical significance as the seat of governance during the colonial and early statehood eras. Route 9 Coastal Heritage Scenic Byway This Scenic Byway, runs in a north-south direction in a course that parallels the western shore of the Delaware River and Bay, winding past a succession of uniquely Delaware landscapes: heavily industrial sites, forests, tidal and non-tidal marshlands, areas of significant natural resources and wildlife habitat, historic towns and quaint villages.