Pennsylvania Route 420 is a short, north–south state highway in Delaware County, Pennsylvania. The route runs from Pennsylvania Route 291 in Tinicum Township, a short distance west of the Philadelphia International Airport, to Pennsylvania Route 320 in Springfield Township.

Pennsylvania Route 420 heads north from Pennsylvania Route 291 on Wanamaker Avenue. Shortly after the PA 291 intersection, Pennsylvania Route 420 features a cloverleaf interchange with Interstate 95. The route then crosses the Darby Creek into the borough of Prospect Park, and the name changes to Lincoln Avenue. Pennsylvania Route 420 intersects U.S. Route 13 in Prospect Park. The route then enters Ridley Township, where it becomes known as Kedron Avenue. Pennsylvania Route 420 crosses MacDade Boulevard and continues north into the borough of Morton. At the intersection with Morton Avenue near the crossing of the SEPTA Media/Elwyn Line, Pennsylvania Route 420 becomes known as Woodland Avenue. Woodland Avenue continues into Springfield Township, intersecting the Baltimore Pike and continues north to Pennsylvania Route 320, a short distance south of U.S. 1.

PA 420 was signed in 1928.[citation needed]

Many of the route's signs have been stolen because of the route number's significance to slang for smoking marijuana.[citation needed]

The entire route is in Delaware County.