Fairfield is a borough in Adams County, Pennsylvania, United States. The population was 526 at the 2020 census.

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.