The 13th congressional district of Pennsylvania is a congressional district in the U.S. state of Pennsylvania. The district contains all of Adams, Bedford, Blair, Cambria, Franklin, Fulton, Huntingdon, Juniata, Mifflin, and Perry counties. It also includes slivers of Cumberland and Somerset counties. Republican John Joyce has represented the district since 2019. With a Cook Partisan Voting Index rating of R+25, it is the most Republican district in Pennsylvania.

Adams County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 103,852. Its county seat is Gettysburg. The county was created on January 22, 1800, from part of York County, and was named for the second President of the United States, John Adams. On July 1–3, 1863, a crucial battle of the American Civil War was fought near Gettysburg; Adams County as a result is a center of Civil War tourism. The county is part of the South Central Pennsylvania region of the state.