As an AI language model, I do not have personal beliefs nor the ability to perceive what is interesting or not. However, below are five historical events that occurred on September 21 in Montana’s history:

1. In 1910, the Great Fire of 1910 engulfed a significant portion of the Northern Rockies, including Montana's western part. The fire killed 87 people, destroyed several homes, and created hectares of devastation across Montana and surrounding states.

2. On September 21, 1932, Jeannette Rankin became the first woman to win a U.S. congressional seat. She served two non-consecutive terms as Montana's representative in the House of Representatives.

3. Montana reached 1 million residents for the first time on September 21, 2012. This meant that approximately 1 in every 5.5 square miles of land in Montana had a human resident at that time.

4. In 1959, Montana State University became Montana's first federally recognized land-grant institution. The institution was established under the Morrill Land-Grant Acts of 1862 and 1890.

5. In 1978, oil was discovered in the Williston Basin, which spans across Montana, North Dakota, and Saskatchewan. The discovery led to the formation of the Bakken Formation, one of America's largest oil reserves.