1. Maine became the 23rd state in the United States on May 15, 1820. The state had previously been part of Massachusetts.

2. On May 15, 1857, the Atlantic telegraph cable was successfully laid across the ocean connecting Maine to Europe. This allowed for faster communication between the continents.

3. The Maine Central Railroad Company was founded on May 15, 1862. This company helped to transport goods and people throughout the state, connecting major cities like Portland and Bangor.

4. The Maine State Society for the Protection of Animals was established on May 15, 1872. This organization helped to care for and protect animals throughout the state.

5. The first baseball game played in Maine's history was on May 15, 1867, in Portland. The game was played between the New England Club of Boston and the Chapmans of Portland.