Maryland Day is a legal holiday in the U.S. state of Maryland, observed annually on March 25. It commemorates March 25, 1634, when settlers from The Ark and The Dove first set foot on Maryland soil at St. Clement's Island in the Potomac River, the first European settlement in the Province of Maryland and the third English colony to be settled in British North America. First observed by Maryland public schools in 1903, Maryland Day became a legal holiday in 1916, and it is celebrated with ceremonies and historical commemorations across the state.

The Maryland colony was authorized under a charter granted on June 20, 1632, by Charles I of England to Cecil Calvert, 2nd Baron Baltimore (1605-1675). The grant had originally been intended for his father, Sir George Calvert, 1st Baron Baltimore (1574-1632), who had served the King as Secretary of State from 1619 to 1625 despite his conversion to Roman Catholicism, and who had earlier received the title "Lord Baltimore" (named after the town of Baltimore in Ireland) along with a first colonial grant, the Province of Avalon in the Newfoundland Colony. George Calvert died before the Maryland charter was completed, so it passed to his son.

The settlers, about 140 in number, departed from Gravesend on the Thames River downstream from London, where an oath of allegiance to the King was administered to the passengers. Three Jesuit priests, among them Father Andrew White, joined the ships at Cowes on the Isle of Wight, where they avoided having to give the oath of allegiance and supremacy to the King. The expedition was led by Lord Baltimore's younger brother, Leonard Calvert (1606-1647), who became the colony's first governor.

On March 25, 1634, the settlers came ashore at St. Clement's Island (later known as Blackistone Island, now St. Clement's Island State Park), off the northern shore of the Potomac River, which formed the border between the new colony and the earlier English settlements in Virginia. In thanksgiving for the safe landing, Father White celebrated Mass for the colonists, and a large cross was erected. The landing coincided with the Feast of the Annunciation, a holy day honoring Mary, and the start of the new year in England's legal calendar (prior to 1752). The colonists soon sailed back down the river to the southeast and settled a capital at St. Mary's City, near the point where the Potomac flows into the Chesapeake Bay.

The holiday began its official observance in 1903, when the State's Board of Education chose March 25 to honor Maryland history and to increase the teaching of state and local histories in the public schools. In 1916, the General Assembly (state legislature) authorized "Maryland Day" as a legal holiday (Chapter 633, Acts of 1916). Although it remains a legal holiday, Maryland Day was abolished as a holiday for State employees in 1996 (Chapter 347, Acts of 1996).

Ceremonies, activities, historical pageants and other commemorative events are held annually in Historic St. Mary's City in St. Mary's County, the first colonial capital of the province, where the first sessions of the General Assembly of Maryland were held. The site includes several reconstructed provincial and colonial structures, including the first State House, and is operated as a living history museum.

An annual ceremony is held in Baltimore at the base of the 1908 statue of Cecil Calvert on the steps of the west front of the Baltimore City Circuit Courthouse (renamed in 1985 after national civil rights leader Clarence M. Mitchell, Jr., 1911-1984) facing St. Paul Street, with the ceremony continuing inside in a ceremonial courtroom.

An annual Maryland Day weekend celebration is held in the Four Rivers Heritage Area of Maryland, from the State Capital in the City of Annapolis to southern Anne Arundel County. This celebration highlights Maryland's history, heritage, culture and environment at approximately 20 sites with over 40 events during Maryland's birthday weekend. The 2020 celebration was cancelled due to the coronavirus pandemic.