1. On September 23, 1642, Cecil Calvert, the second Lord Baltimore, issued a proclamation declaring that slavery was legal in Maryland. This made Maryland the first British colony to legally recognize slavery.

2. In 1779, during the American Revolution, the Battle of Flamborough Head took place off the coast of Maryland. American naval hero John Paul Jones and his crew captured the British warship HMS Serapis in the battle.

3. On September 23, 1800, the Chesapeake and Delaware Canal Company was incorporated in Maryland. The canal, which opened in 1829, provided a shortcut for ships traveling between Baltimore and Philadelphia.

4. In 1862, during the Civil War, the Battle of Shepherdstown took place in Maryland. Union forces under General Fitz John Porter unsuccessfully tried to stop Confederate forces from crossing the Potomac River.

5. On September 23, 1957, the University of Maryland integrated its undergraduate program. This came after a federal court ruling that declared the university's segregation policies unconstitutional.