What was to become St. Mary's County was land where the Conoy Indians lived. It is located along the shores of the Potomac and Patuxent Rivers, stretching southward to the Chesapeake Bay. The shoreline, 400 miles of waterways, is indented with hundreds of small bays, creeks, rivers and streams. Much of the land has remained farmland, and still has the untouched charm the settlers found over 300 years ago.
Here, the English settlement of Lord Baltimore's Maryland began with the arrival of the passengers who had set sail on the Ark and the Dove from the Isle of Wight on November 22, 1633. They landed at St. Clement's Island in the Potomac River on the southwestern side of present-day St. Mary's County on March 25, 1634. Now, the date of their landing is commemorated annually as Maryland Day . This county was also home to Margaret Brent, the first woman to demand the right to vote. Historic St. Mary's City was the first capital of Maryland.
Because St. Mary's County is close to Washington, Baltimore and Richmond (VA), it has become one of the fastest growing areas in the State. The county seat is Leonardtown.