Saint Mary's County (often abbreviated as St. Mary's County), established in 1637, is a county located in the U.S. state of Maryland. As of the 2010 census, the population was 105,151. Its county seat is Leonardtown. The name is in honor of the Catholic saint Mary, the mother of Jesus as told in the Bible. St. Mary's County comprises the California-Lexington Park, MD Metropolitan Statistical Area, which is also included in the Washington-Baltimore-Arlington, DC-MD-VA-WV-PA Combined Statistical Area.