An Adams County Historical Society was organized in 1888 and continued in operation for almost one year. A second society was organized in 1934 and ceased to function when its president died two years later. The third and present society began meeting in 1939. A charter of incorporation was secured the following year. The county commissioners offered some space in the basement of the courthouse, which the officers used to create a library, archives, and museum. In 1959 the society entered into a 39-year lease of the oldest building on the Lutheran Theological Seminary in Gettysburg. Completed in 1832, this building was last used as a dormitory during the 1953-1954 year. The historical society occupied this building in 1961. Under the terms of a lease which will expire in 2026, -it is the society's present headquarters. The most imposing item in the society's collection is its headquarters, since 1976 named Schmucker Hall, in honor of the seminary's founder. On the morning of July 1, 1863, it was the largest building on Seminary Ridge (the other two being the residences of professors), which was a part of the Union line as the Confederate Army approached from the west and then from the north. During the afternoon the Union troops were forced to retreat through the town of Gettysburg, leaving Seminary Ridge in Confederate hands. The old dormitory became the first field hospital of the battle, into which the wounded of both sides were carried. During the battle, the building suffered some damage, which the seminary authorities were able to repair in time to begin the fall session in late September, about one month after the last of the wounded were removed.

The Adams County Historical Society has often been referred to affectionately as the "county's attic" - an archive and museum preserving the rich cultural heritage of Adams County, Pennsylvania. The Society offers twenty-one hours of public operation utilizing paid and volunteer staff to serve researchers and visitors at its headquarters and museum located in Schmucker Hall or "Old Dorm" on the campus of the the Lutheran Theological Seminary in Gettysburg. The Adams County Historical Society was established to "foster interest in the history of Adams County and vicinity, conduct research, preserve records and objects, mark sites, and pursue such activities as may be related to the history of the community."