1. On September 27, 1787, a convention was held in Hartford to ratify the United States Constitution. Connecticut was the fifth state to ratify the Constitution, following Delaware, Pennsylvania, New Jersey, and Georgia.

2. The city of New Haven was founded on September 27, 1638. The city was an important center for the Puritan church and became known for its educational institutions, including Yale University.

3. On September 27, 1955, the first nuclear-powered submarine, the USS Nautilus, was commissioned at the Electric Boat Company in Groton, Connecticut. The Nautilus was the first submarine to complete a submerged transit of the North Pole.

4. On September 27, 1965, Quinnipiac College (now Quinnipiac University) was officially chartered by the state of Connecticut. The university has grown to become a prominent national institution, with campuses in Hamden and North Haven.

5. On September 27, 2005, Connecticut became the first state in the nation to pass legislation allowing same-sex couples to enter into civil unions. The law granted same-sex couples many of the legal rights and protections afforded to married couples. In 2008, the state legalized same-sex marriage.