Adams County is a county in the U.S. state of Pennsylvania. As of the 2010 census, the population was 101,407. Its county seat is Gettysburg. The county was created on January 22, 1800, from part of York County and named in honor of the second President of the United States, John Adams. On 1–3 July 1863, Gettysburg and its vicinity was the site of the pivotal battle of the American Civil War, and as a result is a center for Civil War tourism.