U.S. Route 20 (US 20) is an east–west United States Numbered Highway in Pennsylvania, which clips the northwestern corner of the state, running entirely in Erie County. While it is part of the nation's longest road, it features the shortest segment of any two-digit U.S. Route in the commonwealth. Although bypassed by Interstate 90 (I-90) as the primary through route in the area, heavy traffic has led to nearly the entire highway being widened to four lanes in width.

Erie County is a county in the Commonwealth of Pennsylvania. It is the northernmost county in Pennsylvania. As of the 2020 census, the population was 270,876. Its county seat is Erie. The county was created in 1800 and later organized in 1803. The county is part of the Northwest Pennsylvania region of the state.