Leonard Calvert and a group of adventurers left Cowes, Isle of Wight in England on November 22, 1633 in two ships, the Ark (a large ship of 400 tons) and the Dove (weighing 40 tons.) A replica of the Dove is at Historic St. Mary's City. On March 25, 1634, they landed at St. Clements Island and religious ceremonies were held to give thanks for a safe voyage to the new land. On March 27th they arrived at the Indian Village of Yeocomico, and purchased it from the Indians for blankets, cloth, knives, trinkets, axes, hoes and other tools. They renamed the village St. Mary's.
By 1642, the town had at least ten houses, a forge, mill and Catholic Chapel. The colonists built homes made of wooden slabs, with roofs made of shingles. In 1664, the Assembly at St. Mary's City passed a law that could be called the first Maryland building code. The law ordered that all houses built in the town should be at least twenty feet square, two and a half stories high and built with chimneys made of brick. Originally, the chimneys had been made of logs. lined with clay. As they aged, they became fire hazards.
In 1676, the famous State House was built. It was torn down in 1829, and the bricks used to build Trinity Church. To celebrate the 300th birthday of Maryland, a replica of the State House was built.
The priceless heritage of St. Mary's City was Religious Toleration. The Calverts made it a cornerstone of their new settlement. The Religious Toleration Act was passed in 1649, giving everyone the right to worship freely.
An Act passed in 1695, established the bounds of St. Mary's County. "St. Mary's County shall begin at Point Lookout and extend up the Potomac River (and Wicomico) to the lower side of Budd's Creek, and so over by a straight line drawn from the head of the main branch of Budd's Creek to the head of Indian Creek in the Patuxent River, including all that land lying between the Patuxent and Potomac Rivers, from the lower side of said two creeks and Point Lookout." In 1695 the capital of Maryland was moved from St. Mary's City to Annapolis and St. Mary's City gradually reverted to a completely rural community.
Many old buildings, churches, and homes still stand in St. Mary's County. In 1943 the Patuxent River Naval Air Station was built on approximately 6500 acres in what is now Lexington Park, the largest community in the county. The Naval Air Station is the home of the Naval Air Warfare Center-Aircraft Division, U.S. Navy Test Pilot School and the Naval Air Test and Evaluation Museum. The museum is open to the public.