1. Statehood Day: December 21, 1907 marked the day that Oklahoma officially became the 46th state in the United States. In honor of this day, it is recognized as Oklahoma Statehood Day and celebrated every year.

2. Largest Tornado Outbreak: On December 21, 2010, Oklahoma experienced the largest tornado outbreak on record for the month of December. A total of 31 tornadoes touched down that day, causing extensive damage and several fatalities.

3. Celebrity Birthdays: A number of famous people were born on December 21 in Oklahoma history, including country music legend, Carl Edwards; actor and comedian, Samuel Newfield; and former NFL quarterback, Sam Bradford.

4. Record Low Temperatures: Oklahoma is known for experiencing extreme weather conditions throughout the year, and December 21 is no exception. In 1989, the state saw record-breaking low temperatures, with some areas dropping as low as -31 °F.

5. Historical Events: December 21 is also notable for several other historical events in Oklahoma's history, including the opening of the first commercial oil well in the state in 1897 and the opening of the Devon Energy Center in Oklahoma City in 2012, which at the time was the tallest building in the state.