1. The first recorded European settlement in Maryland occurred on May 9, 1634, when the ship Arc and Dove landed on St. Clement's Island in the Potomac River. This event marks the beginning of the colony of Maryland, which was named in honor of Queen Henrietta Maria, the wife of King Charles I.

2. On May 9, 1791, the first United States Census was conducted in Maryland. The census was mandated by Article I, Section 2 of the U.S. Constitution and was used to determine the country's population for the purpose of allocating seats in the House of Representatives.

3. May 9, 1861, saw the start of the Civil War in Maryland. This was when Confederate sympathizers attacked Union troops passing through Baltimore. The event, known as the Baltimore Riot of 1861, marked a turning point in Maryland's neutrality during the early part of the war.

4. The first-ever Preakness Stakes horse race was held on May 9, 1873, at Pimlico Race Course in Baltimore. The race is one of the three legs of the Triple Crown of Thoroughbred Racing and is considered one of the most prestigious horse races in the world.

5. On May 9, 1968, the Poor People's Campaign, led by Martin Luther King Jr., began a demonstration in Washington, D.C. The campaign aimed to draw attention to the issues of poverty and unemployment affecting millions of Americans, including those in Maryland.