1. On October 21, 1861, the First Battle of Cabin Creek, which was said to be the largest battle fought in Indian Territory during the American Civil War, took place. Union forces under Colonel James Williams defeated Confederate forces led by General Richard M. Gano.

2. On October 21, 1919, Oklahoma's first governor, Charles N. Haskell, passed away at the age of 54. Haskell had served as governor from 1907 to 1911 and played a key role in the founding of the state.

3. On October 21, 1925, the town of Cushing, Oklahoma, was hit by a tornado that killed 8 people and caused significant damage. The tornado was one of several that struck Oklahoma during that time period, including the infamous Tri-State Tornado.

4. On October 21, 1942, the USS Oklahoma, a battleship in the U.S. Navy, was hit by multiple torpedoes during the Japanese attack on Pearl Harbor. The ship quickly capsized, resulting in the deaths of over 400 crew members. Many of the sailors who perished on the USS Oklahoma were from Oklahoma.

5. On October 21, 1985, Mary Fallin became the first woman to graduate from the University of Central Oklahoma with a degree in political science. Fallin would go on to serve as Oklahoma's first female lieutenant governor from 1995 to 2007 and as governor of Oklahoma from 2011 to 2019.