1. In 1869, One of the first settlements in North Dakota was founded on May 31 at what is now known as Fargo. The town was named after William Fargo, a director of the Northern Pacific Railway.

2. In 1910, the first airplane flight in North Dakota was made on May 31, by John Alexander D. McCurdy, a member of the Aerial Experiment Association. He flew a biplane over the city of Grand Forks.

3. In 1946, North Dakota became the last state in the United States to ratify the 21st Amendment, which repealed the Prohibition of alcohol. This historic event took place on May 31 in the state capital of Bismarck.

4. On May 31, 1970, the Turtle Mountain Band of Chippewa Indians declared their sovereign authority over their reservation lands in North Dakota. This action was taken in response to the federal government's failure to recognize their treaty rights and land claims.

5. In 1999, the final section of Interstate 94 in North Dakota was completed on May 31, connecting the cities of Fargo and Bismarck. This highway serves as a major artery for transportation and commerce in the state.