Delaware Route 261 (DE 261) and Pennsylvania Route 261 (PA 261), also known as Foulk Road, is a 6.63-mile (10.67 km) state highway running through Delaware and Pennsylvania. DE 261 runs 4.37 miles (7.03 km) through New Castle County, Delaware from an interchange with U.S. Route 202 (US 202) and DE 141 north of Interstate 95 (I-95) near Fairfax, Delaware, a community north of Wilmington, northeast to the Pennsylvania state line. The road runs through suburban areas of Brandywine Hundred as a four-lane road south of DE 92 and a two-lane road north of DE 92. At the Pennsylvania state line, Foulk Road becomes PA 261 and continues 2.26 miles (3.64 km) through Bethel Township in Delaware County, intersecting PA 491 in Booths Corner before ending at an interchange with US 322.

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.