In 1831, the Delaware Railroad was chartered and finished a line from Philadelphia to Wilmington. It was built primarily for passenger service but served as a secondary freight route. Years later the Philadelphia, Washington And Baltimore Railroad connected to Wilmington and began delivering freight at an increasing rate. The PW&B bought out the Delaware Railroad and began the rest of its service to Philadelphia. The Philadelphia, Baltimore and Wilmington Railroad began its service in downstate Delaware (called Delmarva) and bought out the PW&B because of the profit the Delmarva branch brought in. The railroad was profitable until the Pennsylvania Railroad and the Baltimore and Ohio Railroad built lines parallel to the PB&W and began to encroach on business; ultimately the Pennsy bought out the PB&W.
By 1870 the B&O built a railroad station in Wilmington, thus causing a positive impact on Wilmington's economy. By 1893 the Pennsy took the PB&W and turned it into a full PRR Line. Before it was only controlled by the PRR but now was considered wholly part of the PRR system. The PRR then built a line to Baltimore and abandoned the old PW&B line. The B&O abandoned the line through Delaware and tore down the station in Wilmington and the PRR built a new, elevated track with station. The old PB&W and PW&B Line was subsequently abandoned and removed.
The tracks in Wilmington are still there but paved over many times. The only evidence of the old NEC is in Newark, DE, where the original station still stands tall.
Thanks to Christian B. for contributing information about this route.