1. Vermont Passes Same-Sex Marriage Legislation (2009) - On April 15, 2009, Vermont became the fourth state in the United States to legalize same-sex marriage. The legislation was controversial and faced opposition from some conservative groups, but ultimately passed through the state legislature and was signed into law by then-Governor Jim Douglas.

2. The First Successful Commercial Cheese Factory in the U.S. is Established (1851) - On April 15, 1851, the first successful commercial cheese factory in the United States was established in Windham County, Vermont. The factory was founded by Jesse Williams and produced cheddar cheese, which quickly became one of Vermont's most famous exports.

3. Vermont Adequacy Laws Go into Effect (1997) - On April 15, 1997, Vermont's Adequacy Laws went into effect, which required all schools in the state to provide "substantially equal educational opportunities" to all students. The legislation was designed to address discrepancies in educational quality between wealthy and poor areas of the state.

4. The Vermont State House Groundbreaking Ceremony Takes Place (1859) - On April 15, 1859, a groundbreaking ceremony was held for the Vermont State House, which is now a National Historic Landmark. The building was designed by Thomas Silloway and was built using Vermont granite and marble.

5. The Vermont Institute of Natural Science is Founded (1972) - On April 15, 1972, the Vermont Institute of Natural Science was founded. The organization is dedicated to the study and conservation of Vermont's natural environment and offers educational programs, tours, and events for the public.