When first designated, the route followed these two roads from the Maryland state line to Wilmington, where it crossed the Delaware River on a ferry to Penns Grove, New Jersey.

In 1928, the route was rerouted at Hares Corner to head east into New Castle and cross the river on a ferry to Pennsville, New Jersey.

US 40 enters Delaware from Maryland west of Glasgow, heading east on four-lane divided Pulaski Highway (which originates in Baltimore).

Past this intersection, the road curves to the northeast, crossing Norfolk Southern's Delmarva Secondary railroad line at-grade.

The route heads through a mix of wooded areas and businesses as it enters Bear, intersecting Salem Church Road/Porter Road.

US 40 continues through suburban development with some farm fields, passing to the south of the Wilmington University Athletic Complex.

The road widens to six lanes at the Walther Road/Glendale Boulevard junction before reaching an intersection with DE 7 in a business area.

After this interchange, the route narrows to four lanes and passes more development and some farm fields, reaching a westbound right-in/right-out with Appleby Road.

Past this intersection, US 13/US 40 becomes North Dupont Highway and passes between Wilmington Airport to the northwest and businesses to the southeast as it runs along the western border of the city of New Castle for a short distance, reaching a partial cloverleaf interchange with the southern terminus of US 202 and DE 141 at the end of the airport property.

The road loses the eastbound combined right turn, bus, and bicycle lane before passing over the Jack A. Markell Trail and reaching an interchange with I-295 in Farnhurst.

[3][4] Here, US 40 splits from US 13 by heading east concurrent with I-295 on an eight-lane freeway maintained by the Delaware River and Bay Authority (DRBA).

The road has an eastbound ramp to Landers Lane before it passes between residential neighborhoods and comes to a cloverleaf interchange with DE 9 north of New Castle.

[11] In 1928, US 40 was rerouted at Hares Corner to head east through New Castle and cross the Delaware River on a ferry to Pennsville, New Jersey.

[27] In 1954, plans were made to replace the intersection with DE 41/DE 141 in Basin Corner with a modified cloverleaf interchange in an effort to reduce traffic congestion.

[31] A year later, the Farnhurst interchange and the bridge approach were upgraded to Interstate Highway standards, and it was designated as part of I-295.

[34][35] In the middle of 1964, work began on a second span at the Delaware Memorial Bridge due to increasing traffic volumes.

[43] Despite this, the American Association of State Highway and Transportation Officials (AASHTO) still had US 301 follow US 40 between DE 896 in Glasgow and I-295/US 13 in Farnhurst.