1. Maine officially became a state on May 17, 1820, after separating from Massachusetts. The statehood was approved by Congress on March 3, 1820, but the official declaration was made on this day.

2. On May 17, 1861, the 5th Maine Volunteer Infantry Regiment was mustered into service during the Civil War. The regiment played significant roles in several battles, including Bull Run, Antietam, and Fredericksburg.

3. The Maine Centennial Exposition, celebrating the state's 100th anniversary of statehood, opened on May 17, 1920, in Portland. The exposition featured various exhibits, competitions, and events that attracted thousands of visitors.

4. One of Maine's deadliest maritime disasters occurred on May 17, 1848, when the steamship Portland sank off the coast of Cape Cod, Massachusetts, killing all 192 passengers and crew on board. The tragedy led to significant changes in maritime safety regulations.

5. May 17, 1954, marked the groundbreaking ceremony for the construction of the Saint Lawrence Seaway, which connects the Great Lakes to the Atlantic Ocean through the St. Lawrence River. The seaway, which opened in 1959, has been a significant economic and transportation route for Maine and other regions.