Southern Maryland, also referred to as SoMD, is a geographical, cultural and historic region in Maryland composed of the state's southernmost counties on the Western Shore of the Chesapeake Bay. According to the state of Maryland, the region includes all of Calvert, Charles, and St. Mary's counties and the southern portions of Anne Arundel and Prince George's counties. It is largely coterminous with the region of Maryland that is part of the Washington metropolitan area. Portions of the region are also part of the Baltimore Metropolitan Area and the California-Lexington Park Metropolitan Statistical Area. As of the 2020 Census, the region had a population of 373,177. The largest community in Southern Maryland is Waldorf, with a population of 81,410 as of the 2020 Census.

Calvert County is a county located in the U.S. state of Maryland. As of the 2020 census, the population was 92,783. Its county seat is Prince Frederick. The county's name is derived from the family name of the Barons of Baltimore, the proprietors of the English Colony of Maryland. Calvert County is included in the Washington–Arlington–Alexandria, DC–VA–MD–WV Metropolitan Statistical Area. It occupies the Calvert Peninsula, which is bordered on the east by Chesapeake Bay and on the west by the Patuxent River. Calvert County is part of the Southern Maryland region. The county has one of the highest median household incomes in the United States. It is one of the older counties in Maryland, after St. Mary's, Kent County and Anne Arundel counties.