The objectives of the Prince George's County Historical Society are:
To foster an understanding and appreciation of the history and heritage of Prince George's County.
The collection, recording, organization, restoration, and preservation of historical data, artifacts and all associated materials relative to Prince George's County and the state of Maryland.
To promote and encourage research into all aspects of Prince George's County history and heritage.
To acquaint and make available to members and the general public historical data and all associated materials relating to Prince George's County through programs and publications arranged or sponsored by the Society.
To encourage and participate in the protection and preservation of historic sites and structures in Prince George's County.

The Society is holds its board meetings in the historic Marietta Mansion and it maintains the Frederick DeMarr Historical Library in the Greenbelt Library on the lower level.