1. On May 15, 1842, the Armed Occupation Act was signed into law, granting settlers who agreed to bear arms the right to settle on public lands in Florida. This led to an increase in migration to Florida and the development of many settlements.

2. In 1863, during the Civil War, Union troops under the command of General Quincy Gilmore occupied Jacksonville, Florida, and began building defenses to protect the city from Confederate attacks. The occupation lasted for the remainder of the war.

3. May 15, 1956, saw the beginning of the 1956 Atlantic hurricane season, which was one of the busiest hurricane seasons on record. The season produced 15 named storms, including Hurricane Flossy, which made landfall in the Florida Panhandle in September.

4. On May 15, 1972, the Sunshine Skyway Bridge over Tampa Bay was officially opened to traffic. The bridge was built to replace an older bridge that had been hit by a tanker ship, causing a section to collapse and killing 35 people.

5. In 2014, May 15 was declared "Gator Day" in honor of the University of Florida's mascot, the alligator. The celebration included a parade, a cook-off, and other events throughout the city of Gainesville.