1. The signing of the Treaty of Fort Pitt occurred on September 3, 1783, officially ending the American Revolutionary War in Pennsylvania. The treaty was signed between the United States and the British Empire, and gave the United States control over all land east of the Mississippi River.

2. On September 3, 1838, the Great Western Railroad opened in Pennsylvania. This 400-mile long railroad connected Philadelphia and Harrisburg with Pittsburgh, allowing for faster transportation of goods and people across the state.

3. The first daily newspaper in the United States, the Pennsylvania Packet and Daily Advertiser, published its first issue on September 3, 1784. The newspaper was founded by John Dunlap, who also printed the Declaration of Independence.

4. The Pennsylvania State University, commonly known as Penn State, was established on September 3, 1855. The university is located in State College, Pennsylvania, and is one of the largest universities in the United States.

5. The iconic children's television show Mister Rogers' Neighborhood premiered on September 3, 1967. The show was created and hosted by Fred Rogers, a native of Latrobe, Pennsylvania. Mister Rogers' Neighborhood aired for over 30 years and became a beloved part of American popular culture.