1. On April 16, 1863, Boise County was established in Idaho Territory. Originally part of Walla Walla County in Washington Territory, the area became Idaho Territory in 1863 and Boise County was created two months later.

2. In 1912, the Boise Train Depot opened on April 16. The depot, which was the largest in the Pacific Northwest and a popular stop for presidents and other political figures, was in use until 1997 and is now listed on the National Register of Historic Places.

3. On April 16, 1943, the Idaho State Capitol building was damaged by a fire which started in the basement. The fire destroyed much of the building, including the original dome, and resulted in a major renovation and restoration project that lasted nearly 20 years.

4. In 1967, April 16 was designated as Idaho State Day. The day is meant to commemorate the state's admission to the United States on July 3, 1890, and to promote awareness and celebration of Idaho's history and culture.

5. On April 16, 1982, the Idaho National Engineering Laboratory experienced a nuclear reactor accident. Although there were no fatalities, the accident caused significant damage to the reactor and led to increased scrutiny of nuclear facilities in the United States.