1. Battle of Monocacy: On June 17, 1864, the Battle of Monocacy was fought in Frederick County, Maryland during the American Civil War. It was a significant Union defeat, but it delayed the Confederate Army's advance towards Washington, D.C. and gave the Union time to prepare for a subsequent attack.

2. Birth of John Wesley: John Wesley, the founder of Methodism, was born in Epworth, England on June 17, 1703. Wesley's teachings had a significant impact on religion in Maryland, with Methodism becoming one of the largest Protestant denominations in the state by the 19th century.

3. Maryland's First Public University: On June 17, 1856, the Maryland Agricultural College (now known as the University of Maryland, College Park) was established by an act of the Maryland General Assembly. It was the state's first public university and has since become one of the largest and most prestigious universities in the region.

4. Chesapeake Bay June Bug: The Chesapeake Bay June Bug, a unique species of beetle with distinctive bright green coloring, emerges from its pupal stage in late June. This insect is found only in a few states along the eastern seaboard and is considered a rare and interesting part of Maryland's natural history.

5. Harry Truman Visits Maryland: On June 17, 1950, President Harry Truman visited Frostburg, Maryland to dedicate a new athletic field at Frostburg State Teachers College (now known as Frostburg State University). The event was significant as it was one of Truman's first public appearances following the outbreak of the Korean War.