St. Mary's County, Maryland  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 Mary, the mother of Jesus. Mary's County comprises the California-Lexington Park, Maryland Metropolitan Statistical Area, which also is included in the Washington-Baltimore-Arlington, DC-MD-VA-WV-PA Combined Statistical Area. It is part of the Southern Maryland region. The county was the home to the first Maryland Colony, and the first capitol of the Colony of Maryland. Settled by English Catholics, it is considered to be the birthplace of religious freedom in North America, at a time when the British colonies were settled primarily by Protestants. The county is home to the Patuxent River Naval Air Station and St. Mary's College of Maryland. Traditionally, St. Mary's County has been known for its unique and historic culture of Chesapeake Bay tidewater farming, fishing, and crabbing communities. But with the advent of the military bases, growth of an extensive defense contractor presence, and the growth of St. Mary's College of Maryland, as well as increasing numbers of long-distance Washington, D.C. commuters, it has been undergoing a decades-long transformation which has seen the county's population double since 1970. The settlement of Lord Baltimore's Maryland began with the arrival of passengers from England at St. Clement's Island in the Potomac River in what is now southwestern St. Mary's County on March 25, 1634 and the annual anniversary of this landing is celebrated as "Maryland Day". The passengers arrived in two vessels, the "Ark" and the "Dove" that had set sail from the Isle of Wight on November 22, 1633. The county is the site of the first Catholic Mass celebrated in one of the original thirteen colonies (after they had become English colonies). Earlier dates of masses being said were during 1526–1527 at San Miguel de Gualdape. Due to the small size of the island and its lack of resources, there was no intention to make a permanent settlement on the island. Instead St. Clement's was used as a base for the settlers while scouting for a more suitable site. This was how a bluff overlooking the nearby St. Mary's River was chosen for numerous reasons, and became the site of the first permanent settlement.