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.

DE 261 begins at an interchange with US 202 and the northern terminus of DE 141 north of Alapocas Run State Park and south of Fairfax in Blue Ball, heading northeast on four-lane divided Foulk Road.

The road continues through the suburban Brandywine Hundred area, passing residences along with a few businesses.

DE 261 remains a four-lane undivided road through this area, occasionally widening into a divided highway at intersections.

Past the Murphy Road/Wilson Road intersection, a church with a park and ride lot is located northwest of DE 261.

[1] PA 261 begins at the Delaware state line and continues northeast on two-lane undivided Foulk Road through Bethel Township in Delaware County, passing through residential areas as it crosses Zebley Road in the community of Zebleys Corner.

North of this intersection, the road runs between a tank farm to the west and Bethel Springs Elementary School to the east prior to crossing Bethel Road and entering wooded residential neighborhoods.