U.S. Route 13 (US 13) is a U.S. highway running from Fayetteville, North Carolina, north to Morrisville, Pennsylvania. In the U.S. state of Delaware, the route runs for 103.33 mi (166.29 km). It traverses the entire north–south length of the state from the Maryland state line in Delmar, Sussex County, north to the Pennsylvania state line in Claymont, New Castle County. US 13 connects many important cities and towns in Delaware, including Seaford, Dover, and Wilmington. The entire length of US 13 in Delaware is a multilane divided highway with the exceptions of the segment through Wilmington and parts of the route in Claymont. Between the Maryland state line and Dover, US 13 serves as one of the main north–south routes across the Delmarva Peninsula. From Dover north to Tybouts Corner, the route is followed by the controlled-access Delaware Route 1 (DE 1) toll road, which crosses the route multiple times and has multiple interchanges with it. US 13 bypasses downtown Wilmington to the east before it heads northeast of the city parallel to Interstate 495 (I-495) and the Delaware River to Claymont. US 13 is the longest numbered highway in the state of Delaware.

New Castle County is the northernmost of the three counties of the U.S. state of Delaware. As of the 2020 census, the population was 570,719, making it the most populous county in Delaware, with nearly 60% of the state's population of 989,948. The county seat is Wilmington, which is also the state's most populous city.